In Milgram's Obedience Experiments, "Teachers" Were LEAST Likely to Deliver

In Milgram's obedience experiments, "teachers" were LEAST likely to deliver the highest levels of shock when

A) the experiment was conducted at a prestigious institution such as Yale University.
B) the experimenter became too pushy and told hesitant participants, "You have no choice, you must go on."
C) the "teachers" observed other participants refuse to obey the experimenter's
Orders.
D) the "learner" said he had a heart condition.