Answer:
A. The students acting as guards became aggressive and cruel.
Explanation:
B. The students were aware of what they were getting into- and signed documents to get into the experiment and were even paid to do so.
C. The prisoners didn't become violent- far from it really, it was the guards who did as t hey were "conditioned" to be more violent after being pressured to do so.
D. It wasn't the guards t hat showed any distress, but the prisoners, some having mental breakdowns and even screaming to be want to be let out.