Answer:
The detail from the sentences given that best supports the theme that people can feel isolated from others is D: Gregor stays home in the evenings.
Step-by-step explanation:
I chose D because the details of Gregor staying home in the evenings show us that he prefers staying alone in his house, without socializing with others. If this is something that happens once in a while it wouldn't mean anything, in fact, it is highly recommended to learn and enjoy spending time with ourselves; but if this is the usual for us, and we are always alone, it becomes an issue. People need to be with other people, we individuals are social animals, and need to be with others in order to be happy. The fact that Gregor stays always home in the evenings give us the clue that he can feel isolated from others.