Evidence in the text you are reading will help you most when trying to understand that text. This evidence will contain definitions, examples, quotes, etc. which will make things clear for you.
B is incorrect as the other works may or may not have anything to do with the text you're reading so they might not help you at all.
C is possible, but the text itself has all the answers - you just have to read it carefully.
D is incorrect because your fellow students may not have the appropriate notes and you should try to work things out on your own first anyway.
The whole sonnet is, in my opinion, about the fact that this woman does not love the poet - she is hiding her feelings well, and thinking about somebody else. So, the correct answer could be either C or D.
