---Look. The man at the gate _____ be our headmaster. He is always standing there every morning.

---No. it ____ be him. He is having a meeting in the office now.

A．must; can’t

B．must; mustn’t

C．can’t; can’t

D．can’t; mustn’t

影响社会分层的主要因素有（）

A.社会分化的必然

B.社会资源有限

C.社会分工的加速

D.社会成员的不平等

E.社会发展的规律