[单选题]

---- 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 the office now.
A．must, can’t B.must, mustn’t C.can’t, can’t D.can’t, mustn’t

---- 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’t, can’t D.can’t, mustn’t