D. An essay that relates an activist's experiences fighting for civil rights
Literary nonfiction consists of any writing based on real-life events but using literary techniques, that is to say, it puts emphasis on the precise and skilled use of words and tone.
Option D is the correct one because in this type of prose is very common to find people's own experience in essays, which are written in a more sophisticated way. In this case, it's about an activist telling his/her real experience fighting for civil rights (a real everyday struggle for a lot of people nowadays).