Baaaaaaaa.

Thank you so much for the kind words yet again, Manuel! And congratulations on surviving the whole series. Have fun studying, and keep us posted on your progress! We're rooting for you. - Charles

@@GMATNinjaTutoring​​Hey Charles, after 6 months and a few attempts, today I entered the 700 club only a few days removed from the discontinuation of the GMAT (700 V38 Q48). I constantly referred back to your and your crew’s sentence correction videos. We are beyond blessed to have a guy like you in the community providing all this free value. Best of luck to GmatNinja and a big old hug from Portugal.

Haha, thank you so much for the kind words! Please don't feel guilty AT ALL -- we're legitimately happy that we can do something useful for people for free. Have a blast studying, and keep us posted on your progress!

​@@GMATNinjaTutoring You guys are awesome

@@mohd.arbazashraffatmi8589 Ah, so you're not too far off! It's really hard for me to even guess what might move the needle a few more points on verbal -- I'd need to look inside your head to figure that out. This video might give you some interesting food for thought, though: kzfaq.info/get/bejne/e6x8jbqUnLPcc4U.html. Some things are easier to fix than others -- hopefully you're dealing with more of the first two factors in the video (both of which tend to be the focus of our verbal videos), and not too much of the last two factors? Again, just food for thought. I hope that helps a little bit, and have fun studying!

Thank you so much for taking the time to write this, and sorry for my ludicrously slow response! Holy smokes, that's an incredible score, and you deserve a huge, huge cookie. I'm honored that we could help a little bit, but if you're capable of a 760, you're obviously really, really talented. So please take a bow. Congratulations again! And let us know where you land for b-school -- somewhere awesome, I'm sure. :) All the best, Charles

I'm so glad that it helped a bit, John! Thank you so much for the kind words. Have fun studying, and please keep us posted on your progress! We like good news. :)

I love this. Congratulations on the improvement, and thank you so much for the kind words, Sana! I'm glad that we could help a bit.

You're awesome, thank you so much for the kind words, Sanam! That made my day. Have fun studying, and keep us posted on your progress! - Charles

hey man how much did you score on verbal and GMAT overall?

You're awesome, thank you so much for the kind words! I'm honored that we could help a bit. Have fun studying, and let us know how things go for you! - Charles

Thank you so much for the kind words, Elenah! I'm so happy that we've been able to help a bit. Have fun studying, and good luck on your exam!

@@GMATNinjaTutoring Thank you

Exactly! +1

Question 2 is admittedly a pretty nasty question, and I don't think anybody really loves the right answer. Personally, I would never write the "correct" version of the sentence in real life, even if I were a journalist specializing in, um, livestock or something. That's why we included it in the video -- it's a tough one. Let's start with the parallelism. In (A) and (B), we have "in part... and partly..." Since "in part" is a prepositional phrase and "partly" is an adverb, we have shaky parallelism, in addition to other potential problems that I didn't bother discussing in the video. Those two are fairly easy to eliminate. So what happens when we take a similar approach to the parallelism in (E)? Well, we have "partly [clause 1]... and partly [clause 2]." Yes, the two clauses are structured differently, and the result arguably sounds terrible. But "sound" doesn't matter on the GMAT, and I don't think we can conclude that the parallelism is WRONG, exactly: both parts start with an adverb, followed by a clause. That seems OK, even if it's not ideal. Since the parallelism isn't clearly wrong, we can focus on meaning in those last three options. And as discussed in the video, it doesn't make a ton of sense to say that breeders are using a technique because they SHOULD acquire certain characteristics. They're doing it in order to acquire certain characteristics. So it's not that we're prioritizing meaning over parallelism, exactly. It's just that the parallelism isn't definitively wrong in (E), and that leaves us with the meaning issues as the determining factor. I hope this helps a bit, and apologies for my slow response!

Thank you so much, Rahul! I'm glad that our rants about idioms and awkwardness and clarity/concision resonated a bit, and I obviously agree with everything you're saying here. :) Have fun studying, and keep us posted on your progress!

@@GMATNinjaTutoring Thanks. I will keep you posted :)

You're awesome, thank you so much for the kind words! It's hugely appreciated. Have fun studying, and please let us know how things go (or went?) for you!

Thank you so much for the kind words, Arka! It's arguably a great sign that you got a 38V but struggled a bit on SC -- your reading skills must be strong, and if that's the case, your "ceiling" on verbal is probably high. Good luck on your exam, and let us know how it goes! We're rooting for you. - Charles

Thank you for the kind words!

I'm struggling with the same thing here, went with D over E for that parallelism issue... I think ultimately the 'meaning' triumphs everything, and it's that cause-effect relationship in E 'partly to' that wins over the informal 'should' in D?

Hi, first of all, there's no reason to take 'partly because' as the two branches of the parallelism structure. If we look at the non-underlined portion, the second branch of the parallelism structure is of the form - 'partly because' + independent clause (crossbreeding is said to provide hybrid vigor). We can also look at the non-underlined portion as 'partly' + dependent clause (because crossbreeding is said to provide hybrid vigor). If we look at sentence D, the structure is - 'partly because' + independent clause ( certain characteristics should be acquire by their steers). If we look at sentence E, the structure is - 'partly' + dependent clause ( to acquire certain characteristics in their steers). D and E are both parallel structures depending on how we construct them, the rest is down to meaning. Option E converts both the stems to 'partly' + dependent clause, and more importantly, the infinitive 'to' drives home the intended meaning of the sentence.

Thank you, Sevinch!

You're awesome, thank you so much for the kind words! I'm honored that we could help a bit. Keep us posted on your progress, and good luck on your exam!

Thank you for watching, Adhirath!

Thank you so much for taking the time to write this, Tarun! You're making me blush. Good luck with your studies, and keep us posted on your progress!

Oh wow, I hope they were tears of... joy of some sort? If I were in your shoes, I would cry tears of relief at the end of this particular video, because I'd be like "oh good, I don't have to watch that big-nosed dude babble incessantly anymore!" ;) All joking aside: thank you so much for taking the time to write this. I'm honored that you made it through everything. Have fun studying, and let us know how everything goes for you!

Hahahaha. I can relate. The feeling is similar to what one feels when his favorite Netflix binge-watch gets over

You're awesome, thank you so much for the kind words, Chanavi. Have fun studying, and keep us posted on your progress!

@@GMATNinjaTutoring I took the exam today and scored 680 (Q47 V36) my verbal improved significantly from my first exam (V27) thanks to your team and the SC playlist!

@@chanavijarutas809This is awesome, congratulations! A nine-point improvement is a TON on verbal, and you deserve a cookie. :) Congratulations again, and have fun with your applications!

Thank you so much for the kind words, @TheAqes! I'm honored that we could help a bit. Keep us posted on your progress, and have fun studying!

Thank you so much for the kind words, Leticia. Have fun studying, and please keep us posted on your progress!

Thank you so much, Maryah! I'm honored that we've been able to help a bit. Have fun studying, and keep us posted on your progress!

Haha, I'm glad that we read your mind accidentally. 😃 Thank you so much for the kind words, and have fun studying, Abhishek!

Thank you for the kind words, Sarthak. Have fun studying, and let us know how things go for you!

Thank you for all of your positivity, Salvador! Keep us posted on your progress -- we're rooting for you. :)

same query

You cannot really say "An eight-inch plaster model is recently discovered". "Discovery" here is not ongoing but a one time event that occured in past and usage of "was" makes more sense than "is".

@@abhishek_pathania Thanks for clearing the doubt 😀

Thank you so much, Salome! I'm glad that you're actually having fun watching this stuff. I usually assume that our viewers must be masochists. ;) Have fun studying, and keep us posted on your progress!

Haha, thank you! I'd be a much happier wizard if I could turn cardboard into chocolate, though. Have fun studying!

The word "although" just introduces some sort of contrast between two clauses, but there's no reason why the two clauses need to focus specifically on different nouns. For "although" to be appropriate, all you need is for two clauses to imply some sort of contrast -- and that's it. I hope that helps!

@@GMATNinjaTutoring I have the same problem. In the previous question we were trying to emphasize in the slime in the two clauses, so why didn't we do the same here?

I'm not 100% sure that this is the issue, but I think you might be confusing the phrase "have been lost" with "having been lost." They sound similar, but they're very different. "Have been" is in the present perfect tense, and it indicates an action that starts in the past and continues into the present in some way. "Having been" (or more generally, "having" + past participle) is a different animal. It's actually a modifier, and it's used to describe an action that starts in the past before something else happens. For example: - "Having been exposed to too much radiation as a child, Tim glowed in the dark until his 21st birthday." Tim was exposed to radiation first, and subsequently glowed in the dark. In answer choice (C) in the Michelangelo question, "having been lost" seems to express a perfectly logical timeline. The model was lost for 300 years, and now it has been discovered. That's OK, and we can move on to other issues. For more on GMAT verb tenses, check out this video: kzfaq.info/get/bejne/qa5ghbx52beUmYU.html. I hope that helps!

@@GMATNinjaTutoring Hi , thanks for the video :) In this question why are we using 'have been used' when model is singular ?

Congratulations on making it through the series! The questions in this video are TOUGH, so 50% is actually pretty darned good. Have fun studying, and thank you again for all of your positivity with the comments! I've probably written this to you before, but please keep us posted on your progress. - Charles

@@GMATNinjaTutoring Definitely. Your videos have been a great help in my prep. I have watched many of them over and over again. I find them better than videos of some of India-based test prep companies, as those videos go too deep in the companies’ quest for meaning-based analysis, bordering on doing a PHD on each question, overwhelming the one watching them and making, in turn, GMAT sound many times more difficult than it really is.

Thank you for the kind words, Karanjeet! I'll start with the last question first: if you've already done all of the SC from recent editions of the OG and verbal guide, I'd recommend picking up a copy of much older editions -- OG 12th ed. and Verbal Guide 2nd ed. would probably be best if you can find them. About 1/3 of the questions will be familiar from the newer (2021/22) editions, but the rest will hopefully be new to you. If you get truly desperate, you can use the question banks from the first two official practice tests at mba.com -- those question banks are floating around on GMAT Club, and hopefully aren't too hard to find. Just be very, very careful with them: don't touch them until after you're 100% certain that you'll never take those first two practice tests again. Otherwise, you'll badly skew the practice test experience, and that's not worth it. That pronoun issue has been a thorny one over the years, and I'm guilty of overstating it in a (disturbingly popular!) live video that I filmed back in... 2017, maybe? Even back then, the punchline was that the subject of a clause CAN refer back to the subject of a previous clause without causing an ambiguity problem -- but it doesn't NEED to refer back to it. I think the messaging in this 2022 video is clearer and simpler (and arguably more accurate): kzfaq.info/get/bejne/f8tzgpdp2d7Oc2w.html. Maybe check that out? I hope that helps a bit!

Good question. Honestly, I'm not so sure that "having been" gives us a bulletproof opportunity to eliminate anything in this particular question, though it's certainly not great, especially in (C). Generally speaking, "having been" feels a bit like the past perfect. It usually denotes an action that occurs before some other action. Something like this would be fine, for example: - "Having eaten too many carrots for dinner, Kian developed an odd orange skin tone at bedtime." The timeline makes sense, right? The guy ate too many carrots first, then developed an orange glow later. In that last question in the video, I'm not 100% sure that "having been" is wrong. That phrase appears in (C) and (E), and if we rearrange those answer choices to isolate the verb tenses, here's what we get: (C) after having been lost for nearly 300 years, a plaster model has been discovered (E) after having been lost for nearly 300 years, a plaster model was discovered Do I love either of these? No -- they both seem a bit off to me. But are they absolutely WRONG because of the use of "having been"? I'm not so sure. (E) has all sorts of other problems, but the verb tense and use of "having been" seems acceptable -- at the very least, the timeline is fine. I really don't like the pairing of "having been" and "has been" in (C), but I'm also not convinced that it's absolutely WRONG. In other words: yes, I think you're onto something, and these aren't great. But at most, I would consider these a little vote against (C) and (E), and I'd keep looking for more concrete issues. I hope that helps a bit!

I hear you on this, Toby: the correct answer is pretty awkward, and far from ideal. It's a weird sentence, and I can't blame you one bit for thinking that (E) isn't great. I guess the takeaway is that you'll want to be very careful about creating rigid definitions of prepositions. The word "in" doesn't always strictly mean that something is physically enclosed in something else. We could be expressing inclusion or involvement, or some other description: "I was in a theater company" or "I read it in a magazine" or "The Jets general manager looks for certain qualities in the quarterbacks he drafts." Was I literally inside the theater company? Was I literally inside the magazine? Are the qualities literally inside the quarterbacks? Not exactly, but these phrases are pretty standard usage. Prepositions are slippery like that, and often have dozens of different definitions. Do I think "in" is a great choice for the sentence about the steers? Personally, I don't think so, but it isn't THAT far off, either. It's the type of thing that should probably make you hesitate, but you don't want to automatically eliminate anything based on it. The use of "should" in (D) is a much clearer problem. If you're not convinced by the explanation in the video, there's a written version here: gmatclub.com/forum/in-recent-years-cattle-breeders-have-increasingly-used-crossbreeding-128059.html#p1990178. I hope that helps a bit!

@@GMATNinjaTutoring Thanks so much Charles! Really appreciate your detailed explanation :)

I would be very, very careful with that line of thinking. The subject of the 2nd clause doesn't AUTOMATICALLY refer back to the subject of the 1st clause. It's just that when the 2nd clause starts with a pronoun, it's likely to refer to the subject of the 1st clause -- but it certainly doesn't have to. If you haven't already seen it, this pronoun video might be worth a look: kzfaq.info/get/bejne/f8tzgpdp2d7Oc2w.html. The punchline is basically that if a pronoun has a reasonable antecedent somewhere in the vicinity, you shouldn't automatically eliminate it. That's why I went through all of those meaning-based gymnastics in the hagfish question: sure, the pronoun is arguably ambiguous in many (or perhaps all) of the answer choices. But that's not a very strong reason to eliminate options, unless there are no other differences between the answer choices. Instead, it's much safer to rely on meaning and logic in this particular question -- and in quite a few others on the GMAT and EA. I hope that helps a bit!

Interesting question! In this case, I don't think the word "recently" is very important in (C). The rest of the sentence gives us a pretty clear idea of the timeline: after the model was lost for 300 years, it "has been discovered". At the very least, (C) is 100% clear that 300 years passed between Michelangelo's use of the model and when it was found. Would that change if we added the word "recently" to (C)? I don't think it changes anything at all, really. Sure, it would clarify that the model was found in modern times (instead of, say, 100 years ago -- which would put Michaelangelo's use of the model closer to 400 years in the past). But does that really matter? I'm not sure that it does -- either way, several centuries elapse between the use of the model and its discovery. And that meaning makes perfect sense. Also, keep in mind that there's nothing special about (A), and we're not trying to "preserve" the meaning of (A). We're just looking for the answer choice that does the best job of expressing a clear, logical statement of some sort. And for the reasons described in the video, that's still (C) -- it's the most logical of the bunch. :) I hope that helps!

@@GMATNinjaTutoring Thank you so much for the reply! It could be that I was tired that day when I saw the video and hallucinated different meanings to the sentences but I see it clearly now. I ended up taking the GMAT this week and got a 710 with a Q48 V40! Just a month ago I was stuck in the low V30. So I cannot thank you enough for the wonderful videos!

@@kkp1023 That's amazing, congratulations on the awesome score and the huge improvement! Seriously, it's really, really hard to make an 8-10 point leap on verbal, even under the best of circumstances. The fact that you pulled that off in just a month is incredible, and it's a rarer achievement than you might think. So I hope that you've celebrated appropriately, Krishnakumar! Good luck with your applications, and please keep in touch and let us know where you land. - Charles

Broadly speaking, your approach sounds completely fine. In practice, your goal on SC isn't to label each answer choice as absolutely "right" or "wrong" in a vacuum -- you're trying to find the best of the five options. So we generally advocate looking for easy eliminations first, and then comparing the remaining choices based on meaning -- and that's what you'll see in our SC intro video (kzfaq.info/get/bejne/oL1yla57ubOaaZs.html). It's also totally fine to skip around among the answer choices, instead of addressing them in order. In this particular video, I still compare answer choices quite a bit, but for the sake of making the video easier to follow, I try to dig a bit deeper into the meaning of each choice individually. But fundamentally, we don't need to prove that four answer choices are WRONG, exactly -- we just need to be confident that the fifth option is better than each of the others. So as long as you're clear about why one answer choice is better than another, your approach sounds spot-on. I hope that helps!

Thank you for the kind words, Rishabh! A couple of other test-takers asked a very similar question, so I'll steal liberally from my response: Question 2 is admittedly a pretty nasty question, and I don't think anybody really loves the right answer. Personally, I would never write the "correct" version of the sentence in real life, even if I were a journalist specializing in, um, livestock or something. That's why we included it in this particular video -- it's a tough one. Let's start with the parallelism. In (A) and (B), we have "in part... and partly..." Since "in part" is a prepositional phrase and "partly" is an adverb, we have shaky parallelism, in addition to other potential problems that I didn't bother discussing in the video. Those two are fairly easy to eliminate. So what happens when we take a similar approach to the parallelism in (E)? Well, we have "partly [clause 1]... and partly [clause 2]." Yes, the two clauses are structured differently, and the result arguably sounds terrible. But "sound" doesn't matter on the GMAT, and I don't think we can conclude that the parallelism is WRONG, exactly: both parts start with an adverb ("partly"), followed by a clause. That seems OK, even if it's not ideal. Since the parallelism isn't clearly wrong, we can focus on meaning in those last three options. And as discussed in the video, it doesn't make a ton of sense to say that breeders are using a technique because they SHOULD acquire certain characteristics. They're doing it in order to acquire certain characteristics. So it's not that we're prioritizing meaning over parallelism, exactly. It's just that the parallelism isn't definitively wrong in (E), and that leaves us with the meaning issues as the determining factor. I hope this helps a bit!

In both (A) and (C), the first clause is dependent, since it starts with "although." I imagine that the confusion stems from the fact that "although" is followed in (A) and (C) by somewhat complex structures. If it helps, ignore the "when threatened" phrase for a moment, since that's just a modifier -- you'll be left with just a simpler, dependent clause in each of those answer choices. Give that a try, and let us know if it doesn't help!

Haha, thank you so much, Kshitij! I'm honored that you enjoyed this one. Have fun studying!

same query

Yes, GMAT doesn't test the difference between Which and That . The second video on Modifiers, the tutor says that.

had the same query, then checked the which and that video, @elenahk7315 is correct.

Here's the relevant chunk of (A) again: "Michelangelo, it is believed, had made his sculpture of David using an eight-inch plaster model that was recently discovered..." The past perfect tense ("had made") generally indicates an action that happened in the past, but before some other action in the more recent past. So for past perfect to be correct, we need something else to happen afterwards -- but still in the past. In this case, "Michelangelo had made his sculpture" before the eight-inch plaster model "was recently discovered." That makes sense: Michelangelo made the sculpture way before the model was discovered, right? So the past perfect tense is fine here. For more on the past perfect tense and other scintillating GMAT verb tenses, check out this video: kzfaq.info/get/bejne/qa5ghbx52beUmYU.html. I hope that helps!

@@GMATNinjaTutoring thank you so much! This really helped🙏

Yup, that's correct! Here's the full version of (E) again: (E) It is believed that Michelangelo used an eight-inch plaster model for his sculpture of David, and it was recently discovered after having been lost for nearly 300 years. There's nothing inherently wrong with this structure, and you're correct that it's two independent clauses joined by an "and." As discussed in the video, there are plenty of flaws with (E), and you could add the structure to the list as a minor issue -- I'm not sure why we would want to separate these ideas into two completely separate clauses. It makes more sense to keep those ideas connected, which is what we see in (C): "believed to be used by Michelangelo" is a modifier, and then the phrase "has been discovered..." is the main verb. That's clearer and easier to understand than the structure in (E). I hope that helps a bit!

Our verbal videos are pretty comprehensive for all three question types, and they cover all of the content and techniques that you really need to know for the exam. The only obvious omission is that we don't assign specific homework in the videos, and you'll need to practice plenty of official questions if you want to improve significantly. But other than that, our verbal videos should be enough, as long as you're able to put our advice into practice -- and that's the hard part, of course. :) I hope that helps, and have fun studying!

Here's the relevant chunk of (C) again, with a few less-important bits removed: "An eight-inch plaster model believed to have been used by Michelangelo has been discovered..." I think the confusion might come from the fact that "believed" looks like a verb, but it's actually a modifier. Here, have some other examples: - "Tim believed that Paul Reed would win the NBA MVP award in 2021-22." "Believed" is a past tense verb, since Tim performs the act of "believing" something. No problem there. But now check out these two sentences: - "Tim, surrounded by piranhas, regretted his decision to wear fish-scented socks." - "Tim, believed to be descended directly from Neanderthals, frequently snacks on cardboard." In the first sentence, it's hopefully clear that "surrounded" isn't a verb at all -- it's just a modifier, describing Tim at that particular moment. The second sentence feels different, but it's very similar structurally: Tim isn't performing the act of believing something. Instead, we're describing Tim, and saying that he has the general reputation of being descended from Neanderthals. So "believed" is a modifier here. The same is true in the Michelangelo question. There's a general belief (held by unnamed people who apparently aren't important enough to be mentioned in the sentence) that the model was used by Michelangelo, so we can use the phrase "believed to have been used by Michelangelo" to describe the model itself. So "believed" is part of the modifier, and not a verb at all. For a longer rant on "-ed" words, check out this article: gmatclub.com/forum/experts-topic-of-the-week-5-15-17-fun-with-ed-words-240280.html#p1854172. I hope that helps!

Yup, I think you might be overthinking, in a way. That particular interpretation of (E) is quite a stretch, unfortunately. For starters, we already know that "cattle breeders" are using crossbreeding -- so it's unreasonable to think that the breeders are acquiring their own characteristics. And even if you think that (E) could still imply that the characteristics are for the breeders themselves, it's hard to see how any of the other answer choices are necessarily better. In (D), for example, you could still interpret the sentence to suggest that the cattle acquire the characteristics FOR the breeders. In other words: if you think that the sentence might be saying that the characteristics are for the breeders themselves, it's still probably a non-issue, since none of the answer choices clearly fix that potential issue. Instead, you'll want to focus on the meaning differences between (D) and (E), and you'll want to keep that analysis as concrete as possible. As discussed in the video, the meaning difference between these two answer choices is subtle, but significant: "should" implies some sort of obligation or duty, and usually implies some sort of judgment by the speaker (e.g., "you should eat more vegetables"). It doesn't make a lot of sense to say that breeders employ certain practices "because they SHOULD" acquire characteristics in their steers; they employ those practices TO ACQUIRE those characteristics in their steers. But again: every question in this video is, by definition, subtle and challenging. So don't lose too much sleep over this one. :) I hope that helps!

I'm not sure that I understand your question fully, but I'll do my best with it! Don't overthink the function of the word "it". "It" is always a pronoun (not a modifier) and when you see it on GMAT SC, you'll want to look for a singular noun that "it" refers back to. If there's no singular noun that makes sense, you have a problem. If there's a singular noun somewhere nearby that actually makes sense, it's probably fine. That's pretty much it. From there, you can move on to other issues. I hope that helps a bit!

You might be overthinking this, in a way. When you see the modifier beginning with "that", just ask yourself: is there something nearby that the "that" phrase could reasonably modify? In this case: is it reasonable to say that the plaster model "was recently discovered after being lost for nearly 300 years"? Sure. The thing was lost for 300 years, and it was found recently. Is it also reasonable to say that Michelangelo originally made his sculpture with that same centuries-old object? Sure. The plaster model has been around for a really long time, and there's nothing wrong with describing the model's adventures both in the distant past (Michelangelo used it centuries ago) and in the much-more-recent past (it was recently found). I hope that helps a bit!

Our videos will continue to premiere every Friday morning at 10:00 a.m. U.S. Eastern time until we've finished a complete series for both quant and verbal. They aren't livestreams, though -- we record the videos in advance, and just premiere them at the same time each week. We have about 16 RC and CR videos remaining before we complete our GMAT and EA verbal series, so the last one should premiere near the end of 2022. Have fun studying, Anmol!

@@GMATNinjaTutoring thanks😊

Sorry to hear that you found this video deflating! To be clear: these are HARD questions. That's the whole point of the video. So if you're 100% comfortable with everything we've covered in the other 17 videos in this series, you're still in really good shape. Getting better at the super-hard, meaning-based questions is a process, and it can take some time to get really good at them -- and depending on your goals, you might not need to be great at them, anyway. :) I hope that helps a bit, and good luck with your studies!

If I understand your question correctly, I think you're referring to the idea that "has been" -- or any other verb in the present perfect tense (has/have + past participle) -- indicates an action that starts in the past and continues into the present. Strictly speaking, that seems odd in question #4: it seems like we discover something once, and that's it. As discussed in the video (and also in our video on verb tenses: kzfaq.info/get/bejne/qa5ghbx52beUmYU.html), there's quite a bit of flexibility when it comes to the use of the present perfect tense in English. In many cases, you could use either the simple past tense (i.e., "was discovered") or the present perfect tense ("has been discovered") -- and it's just a matter of the writer's or speaker's taste. For example, we often say things like "I have visited Namibia" -- even when I'm not actually in Namibia. I'm not necessarily implying that I'll go back to Namibia (though I would love to, because that place is freaking gorgeous), or even that I still feel the effects of the trip today. It's just that we sometimes use the present perfect tense to indicate actions that happened at some unknown time in the past, especially if it's not really important to specify when, exactly, it happened. Same thing is true in question #4: the model "has been discovered" at some unknown point in the past, and the author apparently isn't interested in specifying exactly when it happened. Personally, I would prefer "was discovered" here, but there's nothing wrong with using "has been discovered" instead -- that's up to the author's discretion, as mentioned in the video. The takeaway: if you see the present perfect tense but think it should be past tense instead, don't overreact. Look for other decision points first, because it's not necessarily wrong to use the present perfect for actions that happened solely in the past. I hope that helps a bit!

@@GMATNinjaTutoring That helped. I need to diffrentiate better between definite errors and can be ignored errors.Thanks expert!

@@GMATNinjaTutoring Thanks for this. One that wasn't mentioned in the video was 'to have been used by M' for option C. This jumped out more than the other one for me. I didn't know what to do as it certainly sounds correct when you read it. But you have explained here so I assume same applies for that. Since it was used in the past but does not continue to be used today.