In case if you were to use some of those things in a lifetime. Like using math to be a scientist. Or language arts to write a book.
I'd say D because I think I remember that being a big part of citing works. A could be correct too. I'd look up maybe basic MLA rules and see which ones comes up first. It kinda depends on what your teach emphasizes. Though I'm pretty confident it isn't B or C
He was a spokesperson of his generation because his books mostly spoke about people who experienced suffering due to the gilded age system of values.