This question asks us to infer what must be true based on the information in the stimulus. There are three claims being made here.
1. Some presidents and prime ministers who had very successful foreign policies had no prior experience.
2. Anyone with an acute political sense, a disciplined temperament, and a highly developed ability to absorb and retain information can learn to conduct a successful foreign policy.
3. Prior experience is of little value to conducting a successful foreign policy.
(A) is not necessarily true. We do not know who has more experience. No comparison is made in the stimulus.
(B) must be true. We know that prior experience is not a sufficient condition for conducting a successful foreign policy from the last sentence, and we know that it's not a necessary condition from the first sentence.
(C) is contradicted by the stimulus. We know that prior experience is NOT a necessary condition for conducting a successful foreign policy.
(D) has two issues. The word "anyone" in the second claim ensures that those three elements are collectively sufficient. This answer choice states that they are individually necessary.
(E) is not supported by the stimulus. The first sentence says that prior experience is not necessary, the last that prior experience is not sufficient for conducting a successful foreign policy. It wouldn't make sense then that we should be able to say that a president who has more experience would thereby have more success.