Answer: C. group membership provides the primary means for comparing oneself to others.
Explanation: In instances where there is no objective standards for self-evaluation, individuals often turn to and observe others (usually in a group) in an effort to evaluate our actions, abilities, or opinions by comparing themselves with others. This is known as social comparison. A major motive therefore, for joining groups is that group membership thus provides the primary means for comparing oneself to others, in making sense of ourselves and that of the social world.