Look!The man at the gate _____ be our headmaster .He is always standing there every morning
问题描述：
Look!The man at the gate _____ be our headmaster .He is always standing there every morning
No,it _____be him.He is holding a meeting in the office now.
A.must;can't
B.must;mustn't
C.can;can't
D.can;mustn't
选哪一个 为什么
答
选A
must在这里表判断,意思是一定是
而mustn't只有一个意思,那就是禁止
can在这里也表判断,意思是可能
那么can't的意思也就是不可能