In a Series of Experiments, Stanley Milgram Systematically Varied the Conditions

In a series of experiments, Stanley Milgram systematically varied the conditions of his obedience study. Under which of the following conditions were subjects LEAST likely to continue administering shocks to the full 450-volt level?

A) when the "teacher" and the "learner" were in the same room
B) when the experimenter left the laboratory and gave orders over the phone
C) when the teacher was required to hold the learner's hand down on a shock plate
D) when the teacher observed two other teachers who refused to continue with the experiment