At her health club,Bonnie,who is a skilled runner,runs much faster on the treadmill when other patrons are using nearby equipment.This best illustrates

A) conformity.
B) group polarization.
C) social facilitation.
D) social loafing.

Social facilitation refers to the phenomenon where the presence of others improves an individual's performance on a task they are already skilled at. In this case, Bonnie is a skilled runner who runs faster when she is surrounded by other people at the health club. This is because their presence is increasing her arousal level and causing her to perform better. Therefore, the best choice is C) social facilitation.