What Was a Major Ethical Concern Raised About the Milgram

What was a major ethical concern raised about the Milgram studies?

A) Participants were not aware that they were participating in a psychological study.
B) Participants were compensated very small amounts compared to the stress of the experiment.
C) Only participants belonging to a particular SES background were recruited for the study.
D) Participants learned that they were potentially capable of doing harm to another person simply because they ordered.