You can learn all the three usages of Past Continuous Tense altogether in this video. Everything will be easy and simple when you do it again and again. So, if you practise English regularly, certainly you will acquire it in a short period. Learning Tense is really the first step taken to understand the language. So, Trust that you are going in the right path to attain your goal. It is your foremost duty to do exercise sentences given in the link below.
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And the answer Key for the last class has also been given below in the link.
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Utilize it.