问题

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 theoffice now.
A:must, can’t
B:must, mustn’t
C:can’t, can’t
D:can’t, mustn’t
B:must, mustn’t
C:can’t, can’t
D:can’t, mustn’t
正确答案是: