问题
It _______ be Mr．Johnson who is in the office．— No, it _______ be him．I saw him off at the airport half an hour ago．
A:can’t ; can’t
B:must; can’t
C:must; mustn’t
D:may; mustn’t
B:must; can’t
C:must; mustn’t
D:may; mustn’t
正确答案是：
