To Remove Any Doubts About the Legitimacy of the Shock

To remove any doubts about the legitimacy of the shock generator in Milgram's obedience study, the:

A) "teachers" were given a sample shock.
B) teachers witnessed Milgram being shocked.
C) "learners" were asked to administer a sample shock to themselves.
D) teacher and the learner watched an unsettling short film of a person being shocked at the 220-volt level.