问题
Look! The light in Mr. Brown’s office is still on. He ___________ be working there.—It ___________ be him. He has gone to America.
A:must；mustn’t
B:can；mustn’t
C:must；can’t
D:can；can’t;
B:can；mustn’t
C:must；can’t
D:can；can’t;
正确答案是：
