The correct answer is A. He believed it was inflexible and should not be used over minor conflicts.
President John F. Kennedy was critical of the policy of massive retaliation, which was a Cold War strategy adopted by his predecessor, President Dwight D. Eisenhower. The policy involved the threat of using nuclear weapons in response to any aggression by the Soviet Union or its allies. Kennedy believed that this approach was inflexible and did not provide a proportional response to minor conflicts. He argued for a more nuanced and flexible approach to dealing with potential threats, which led to the development of the doctrine of "flexible response." This doctrine aimed to provide a range of military options beyond the immediate use of nuclear weapons, including conventional forces and limited military interventions.