The statement that most accurately analyzes how the author’s choices in using juxtaposition define the narrator’s perspective is:
The narrator’s feelings of pity and amusement at the old man’s fear emphasize the narrator’s morbid state of mind.
This choice highlights the contrast between the narrator's emotional reaction—feeling both pity for the old man's terror and amusement at it—showing the complexity of the narrator's psyche and his disturbed moral state.