问题
选择题
— It _______ be Jack 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
答案
答案：B
must表推测只用于肯定句；在否定句和疑问句中用can。