In Contrast to Milgram's Original Studies,what Differed in Burger's Recent

In contrast to Milgram's original studies,what differed in Burger's recent replication of the shock obedience studies

A)  Researchers were not perceived as being authority figures. 
B)  Participants were carefully screened and repeatedly told they could stop at any time. 
C)  Participants were very unlikely to conform to experimenter requests. 
D)  The experimental procedure only allowed for verbal reprimands, rather than the provision of shock to the "learners."