What is the purpose of the commentary in the underlined text? to give evidence of stalin’s savage murders to provide examples of stalin’s genocidal actions to explain why stalin became a ruthless murderer to summarize stalin’s time as a communist leader

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's. 

It would have to be c or d