Someone is knocking at the door.It be Tom because he Shanghai already.A.must; has left B.can't;has left
问题描述：
Someone is knocking at the door.It be Tom because he Shanghai already.
A.must; has left B.can't;has left
答
B
答
A
对现在肯定的推测,而can't表示能力
答
B
must 做猜测语气时是“强烈的肯定”语气,翻译可以是“一定是”
can't 做猜测语气时是“强烈的肯定”语气 ,翻译时做“不可能是”解
再对比句子的完整与连贯,还有TOM去上海在说话之前已经发生,故用完成式!
可以得知该句是说“有人在敲门,不可能是TOM,因为他已经去上海了”
所以选B