In a Series of Variations of His Obedience Experiments, Milgram

In a series of variations of his obedience experiments, Milgram found that the subjects were LEAST likely to deliver high levels of shocks when:

A) the experiment was conducted at a prestigious institution, such as Yale University.
B) there was physical and psychological separation between the teacher and the learner.
C) teachers were free to choose the level of shock.
D) the experimenter took responsibility for the learner's well-being.