The Instructor of Your Wine Tasting Class Trips and Falls

The instructor of your wine tasting class trips and falls while discussing the merits of spitting out the wine samples after you have tasted them instead of swallowing them, so as not to get inebriated during the class. You are afraid that he might have hurt himself in the fall, but since no one else in the class is rushing up to help him, you mistakenly believe that the rest of the class thinks the instructor is trying to prove a point about drinking too much in the class. You therefore doubt your own judgement and decide to also not get up to help the instructor back to his feet. This is an example of

A) diffusion of responsibility.
B) pluralistic ignorance.
C) mob mentality.
D) passing the buck.