Mary _______ the piano well. She is often asked to play at the concert. [ &nbs...

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B

c 考查情态动词表示推测。must have done一定做了某事；b=d，所以排除。may have done也许做了某事；句意：—mary的考试分数是班级里最高的。—真的吗？她肯定学习的非常认真。