In Milgram's Original Obedience Study, There Were Many Different Factors

In Milgram's original obedience study, there were many different factors operating in the situation that influenced the subjects to continue obeying the experimenter's orders. Which of the following was NOT one of those factors?

A) The subjects volunteered to participate in the study.
B) The subjects were compensated for their participation when they arrived for the experiment.
C) The subjects knew that their actions were being filmed.
D) If the subject expressed concerns, he was reassured that the experimenter was responsible for the "learner's" well-being.