Final answer:
Social psychologists define a social group as a collection of interdependent people who interact with one another and influence one another. Therefore the correct answer is a and b.
Step-by-step explanation:
Social psychologists define a social group as a collection of interdependent people. This means that the group members interact with one another and influence one another. Social groups are characterized by the interdependence among their members, where each person’s behavior and actions affect the others in the group. For example, in a team sports setting, players interact with each other and their actions on the field can influence the overall performance of the team.