Which of the following was NOT a criticism of Milgram's study?

Which of the following was NOT a criticism of Milgram's study?

a.  It was unethical because the personality traits of the subject were not taken into account.

b.  It was unethical because subjects were deceived.

c.  It was unethical because subjects experienced emotional pain.

d.  It was not a realistic situation and could not be compared to real-world obedience.