It's rather cold in the room. They______ have turned off the steam a few hours ago.
A.should
B.must
C.ought to
D.could

A.A.should
B.must
C.ought
B.could

【参考答案】

B
解析：句意：屋子里相当冷，他们一定在几小时前关闭了暖气。考查must have done结构。这种结构表示对......

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