◎ 题干
Someone is knocking at the door. It            my mother. It's time for her to be back.

[     ]

A. can be
B. may not be
C. must be
D. mustn't be
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“Someone is knocking at the door. It my mother. It's time for her to be back. [ ]A. can be B. may not be C. must be D. mustn't be …”主要考查了你对  【情态动词】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。