Honestly, I know that it is either A. or D. I would most likely go with D.
1. When McMurphy is trying to pull him out of the fog, he realzes that he's not deaf, he started acting like that, because people thought he was too dumb to hear or understand all the thing they were saying, that reveals too why he was so oppressed and hasn't recovered.
2. Chief Bromden is the narrator of the story, he's an obsever since he is deaf and can't talk, he listened all that the people said, but this description of the fog is important because it allow us to understand the state of mind the patients had from Bromden's point of view and according to him, was produced by Nurse Ratched with her strict, mind-numbing routines and humiliating treatment. The character that takes all the patients out of the fog (the oppresion and incapability to recover and be sane aganin) is McMurphy.
