In Philip Zimbardo's Simulated Prison Study

In Philip Zimbardo's simulated prison study

A) the participants were assigned the role of prisoner or guard on the basis of their personality test scores.
B) the participants found it very difficult to play the role of prison guard.
C) the participants were so endangered by their role-playing experience that the study was discontinued after six days.
D) the fair guards protected the prisoners from the "bad" guards..