In Milgram's Obedience Experiments,"teachers" Were Most Likely to Deliver High

In Milgram's obedience experiments,"teachers" were most likely to deliver high levels of shock when

A) the experimenter was perceived to be an ordinary college student like themselves.
B) the "learner" was placed in a different room from the "teacher."
C) they saw that other "learners" disobeyed the experimenter.
D) they saw how "learners" who disobeyed the experimenter were punished.