IELTS Reading: true, false, not given

 Look at the following extract from a text about a psychology experiment:

In the year 1971, Zimbardo accepted a tenured position as professor of psychology at Stanford University. There he conducted the Stanford prison study, in which 21 normal college students were randomly assigned to be "prisoners" or "guards" in a mock prison located in the basement of the psychology building at Stanford. The two week planned study into the psychological impact of prison life ended only after 6 days due to emotional trauma being experienced by the participants.

Are the following statements true, false or not given?

1. The participants in the study were all psychology students.
2. They were given the choice of playing the role of prisoner or guard.
3. A real prison was used in the experiment.
4. The study aimed to investigate the mental and behavioural effects of life in prison.