Final answer:
Shauna demonstrated a 'diffusion of responsibility' by not helping a man in a wheelchair because she assumed that others present would do so. The correct option is c. diffusion of responsibility.
Step-by-step explanation:
In the scenario described, Shauna's behavior, where she does not stop to help a young man in a wheelchair because she assumed someone else would, is an example of diffusion of responsibility.
This is a psychological phenomenon where individuals are less likely to take action or feel less responsible for taking action when others are present.
It is closely related to the bystander effect, wherein the presence of other bystanders reduces the likelihood of any single person helping. It is not an example of prosocial behavior, which involves actions intended to benefit others. The correct option is c. diffusion of responsibility.