In making wedding preparations, jason conforms to the expectations of his future bride's family, in order to win their favor. his behavior illustrates the importance of social influence

I believe the answer is:  normative social influence.
 normative social influence refers to the type of influence that lead us to conform to a certain perspective/tradition that held by the majority members of a social group. The expectation that enacted through normative social influence usually informal and wouldn't be resulted in legal punishment if we choose not to follow iw.