It is very important to know the usages of all the tenses clearly. Then only, we can use the correct tense to the right situation. So, here from this video you can clarify your doubts in using the two tenses Past Continuous Tense and Past Perfect Continuous Tense. Listen to the class keenly and understand the difference between the two tenses mentioned above. Since Practise makes a man perfect, exercise sentences have been given in the link below for your practice.
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And the answer key for the last class has also been given in the link below.
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Utilize it.