Mark Is Walking Down a Busy Street and Sees a Man

Mark is walking down a busy street and sees a man lying unconscious in the gutter. The man is wearing a dishevelled suit and surrounded by empty beer bottles. The other people walking past don't seem notice the man, and the ones that do just laugh at him and move on. Mark is concerned that the man might actually be in trouble-perhaps he has had a heart attack or some other kind of accident? But Mark also wonders if perhaps the man is fine, perhaps he just had a big night on the town? Mark wants to help but Mark also doesn't want to overact in the situation or act inappropriately. The phenomenon that Mark is experiencing is:

A) diffusion of responsibility.
B) fear of social blunders.
C) prejudice.
D) social loafing.