Philip Zimbardo and His Colleagues Established a Mock Prison in the Basement

Philip Zimbardo and his colleagues established a mock prison in the basement of the psychology building at Stanford University.How did they decide which participants would assume the role of "prisoner" and which would assume the role of "guard"?

A) People were assigned at random to each role.
B) Aggressive people tended to volunteer for the role of guard.
C) The experimenters used personality tests to assign participants to roles.
D) Participants who had spent time in jail refused to be prisoners.
E) Because of safety concerns, aggressive people were assigned to the role of prisoner.