Someone is knocking at the door.Who it be?— It be Tom.He is still in the school.A.can,can't B.can,mustn't C.might,could
问题描述：
Someone is knocking at the door.Who it be?— It be Tom.He is still in the school.A.can,can't B.can,mustn't C.might,could D.might,may 为什么B不可以 mustn't不是更加肯定吗?
答
这里是表示推测,表推测否定一般情况下都使用can't .mustn't是指禁止,绝对不可以.must可以表推测,但mustn't 一般不可以表推测,一般用于祈使句或请求语境.