A psychology class has been assigned an individual case study project as well as a group project. The members of the same grade for the group project but will be graded separately for their individual projects. Drew, Ben, Donna, and J one such group. Drew and Donna worked very hard on the group project. Ben and Julia, however, did not contribute project because they felt that Drew and Donna would manage to get good grades for the group project. They focus individual projects instead. Ben and Julia's behavior is an example of:

Self$-$serving bias

Attribution error

Social loafing

Staff validity

Groupthink