Final answer:
Option (A), Zimbardo's prison experiment teaches us that people can act horrifically in adverse conditions and can be overly obedient to perceived authority. The experiment's quick descent into cruelty underscored the power of social roles and the potential loss of personal morality within such contexts.
Step-by-step explanation:
One important lesson we can learn from Zimbardo's prison experiment is that it's possible for people to act horribly in evil situations (A). This experiment, which involved participants role-playing as prisoners and guards, revealed the powerful influence of social roles, norms, and scripts on individuals' behaviors.
The guards' abusive behavior and the prisoners' consequent anxiety and hopelessness became so severe that the experiment had to be halted after only six days. Moreover, the study showed that people are willing to be obedient to false authority (C), even when the authority is merely another participant acting in a role.
However, subsequent criticisms and attempts at replication suggest caution in drawing broad conclusions from the experiment's findings.