Answer:
The correct answer is C. It adds suspense by introducing real, narrowly avoided danger into the narrator's situation.
Step-by-step explanation:
At this point of the story by Poe, the narrator is imprisoned in a dark cell and cannot see anything. The fact that he cannot see his surroundings and that he barely escaped death by falling into a pit adds suspense to the story. There could be more dangers around him but the narrator and the readers cannot see them, so the suspense increases.