our teacher___be in his office because the lights off.A can't B.mustn't选哪个?为什么?

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our teacher___be in his office because the lights off.A can't B.mustn't选哪个?为什么?
our teacher___be in his office because the lights off.A can't B.mustn't
选哪个?为什么?

our teacher___be in his office because the lights off.A can't B.mustn't选哪个?为什么?
A.
can't表示否定的推测,意思是“不可能……”
mustn't意思是禁止,不允许