If this question is supposed to refer to the time period before 1949, D is the best answer. After 1949, A is the best answer.
A is clearly correct for all times during the Cold War. Containment was the doctrine of containing communism where it was and not letting it expand farther. Up until 1949, this would have included China since China was not communist in 1949. Containment was certainly a cheaper way to fight communism than actually going to war to try to destroy communism where it already existed.
Therefore, D is the best answer. However, if you know that you are only talking about the time after 1949, A is the best answer.