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 condition were the subjects LEAST likely to continue administering shocks to the maximum level?

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