Answer: D) the narrator’s feelings about the degenerate human race.
Step-by-step explanation: in literature, a conflict is a struggle between opposite forces, usually between a character (the main character or a very important one) and himself (internal conflict), society or another character (external conflict). In the given excerpt we can see an example of an internal conflict (character vs. self) where the antagonist is the narrator's feelings about the degenerate human race ("it gave me melancholy reflections to observe how much the race of human kind was degenerate among us").