单选题 Which of the following sentences expresses probability?
A. He must have picked up a cold—he's begun to snuffle.
B. We must have a clear understanding of the problem.
C. One must have one's own opinions and not drift with the current.
D. To be healthy one must have an adequate diet.

【正确答案】 A

【答案解析】[解析] 情态动词题。情态动词must除了用来表示命令，必须如何以外，还可表示有依据的肯定推测，意为“一定会……”，对现在情况的推测用“must：+动词原形”；对已经发生的情况的推测则用“must have done”。B、C以及D中的must have都表示“必须要有……”；A意为“他开始鼻塞，一定是感冒了。”因此A为答案。