The passage that best conveys the reason for the narrator's guilt is the one about making someone feel worthless, indicating the emotional impact of the narrator's actions on the grandmother.
The passage that best identifies the reason the narrator feels guilt at the conclusion of the story is the one that mentions the impact of making a person feel worthless. Therefore, the correct passage is:
"Your grandmother says to tell you that of all the hurtful things you can do to a person, the worst is to make them feel as if they are worth nothing."
This passage conveys a deep sense of guilt and remorse because it is a direct address to the narrator about the gravity of their actions, and it implies a profound emotional impact on the grandmother, emphasizing the significance of making someone feel valued.