Listen! David is talking happily with his mother in the next room.　It be his moth

--- Listen! David is talking happily with his mother in the next room.
　--- It be his mother. She has gone to Yunnan to be a volunteer doctor.
A. should
B. must
C. can’t
D. mustn’t

A. shouldB. must(答案→)C. can’tD. mustn’t解析：考查情景交际和情态动词。“听！大卫在隔壁正在高兴地和妈妈谈话。”“她不可能是他的妈妈，她妈妈作为一名志愿医生，已经去云南了。”情态动词可表推测。Should“应该”；must“一定”；can’t“不可能”；musn’t“”禁止不，表推测。故选C。

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