I think it's really difficult to choose one. But in my view both of A and C look like the right ones. It will be good to consolidate these statements together. Because human nature really remains the same but the only thing always changes is the values.
D. These reasons and more are why "Taxi Driver" is widely considered a cinematic classic.
The subject of this poem is <em>Knowing oneself.</em>
I think this because he talks about what he has done and how hes learning to cope with it. Also the Title of the poem is Myself, so that is why the subject is Knowing oneself.
***Correct me if i'm wrong***
Hopefully this will help you out