Which of the Following Is Not an Example of Social

Which of the following is not an example of social influence?

A) A sports fan who decides to join the other members of the stadium crowd in doing the wave
B) A student who hears that some of his fellow classmates may have been exposed to a noxious gas and immediately comes to feel a bit nauseated himself
C) A model who catches a glimpse of herself wearing a swimsuit in a mirror and suddenly becomes self-conscious about the way she looks
D) A guest at a dinner party who does not understand a joke told by the host, but laughs anyway because everyone else is laughing