In a variation on his original experiment, Milgram had the experimenter leave the room after telling ...

In a variation on his original experiment, Milgram had the experimenter leave the room after telling participants that they could deliver whatever level of shock they chose.
 
  After the experimenter left, a confederate suggested that the participant increase the shock by one level each time the learner made a mistake. In this variation, only about 20 percent of participants went to the highest shock level. The fact that the authority figure's presence made much more of a difference than that of a peer suggests the role of
  a. informational influence.
  b. normative influence.
  c. private acceptance.
  d. mindless conformity.