Answer:
C) A narrow raised platform
Step-by-step explanation:
-long enclosed passage would not make sense since the speaker indicates "looking down".
-A building would not make sense because they are not specifying the 'edge' of a building gallery (which would be inside).
-A narrow raised platform would make the most sense since they are looking down onto something.
-Last answer is pointless because there is no indication of other people aside from Cavor and the speaker.