The classroom is empty, so the students______have gone to the laboratory.

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问题 The classroom is empty, so the students______have gone to the laboratory.

选项 A、ought to
B、must
C、should
D、could

答案B

解析 本题考查情态动词的用法。“情态动词+have done”表示对过去行为的推测。根据句意,must have done符合题意,是对过去行为的肯定推测。ought to/should have done sth.意为“过去应该做某事却未做”;could have done sth.用于虚拟语气,意为“本来能够做某事却未做”。
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