The correct answers would be option C: " It expresses his nearly subterranean sense of isolation" and option D: "It illustrates how he leads an almost subhuman existence". In the excerpt, the author is describing the character's home and comparing it to animals lair's, animals that keep to themselves in nature, therefore one can infer that the character also keeps to himself (in isolation) and that he possess animal qualities that make it seem he leads a subhuman existence.
Options A and B are incorrect because the author does not give any reference in the excerpt so as to assume the character is single minded or looking to the future.
