Stanley Milgram's research on obedience is most relevant to which of the following historical scenarios?
a) Abraham Lincoln was elected 16th president of the United States of America.
b) The Cuban Missile Crisis took the United States and Russia to the brink of a catastrophic war.
c) The space shuttle Challenger was permitted to take off even though many believed it had dangerous design flaws.
d) During the Holocaust, guards at concentration camps killed prisoners because they were ordered to do so.