The correct answer is similarity bias.
Similarity bias refers to the phenomenon where we express a preference or show preferential treatment towards something or someone who is similar to us, rather than something or someone who is different from us. Results from this experiment indicated that "straight" or conservatively dressed confederates were more likely to be given change by college students who were dressed similarly. Similarly, "hip" confederates were more likely to be given change by similarly dressed college students, demonstrating the similarity bias.