---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

下图中交换机同属一个VTP域。除交换机B外，所有交换机的VLAN配置都与交换机A相同。交换机A和B的VTP工作模式的正确配置是（）

A．set vtp mode transparent和set vtp mode server

B．set vtp mode server和set vtp mode transparent

C．set vtp mode server和set vtp mode client

D．set vtp mode server和set vtp mode server