— I phoned you yesterday morning. A girl answered, but I didn’t recognize the voice.

— Oh, it __________ my younger sister. She was in my room at that moment.

A．must have been

B．should have been

C．could have been

D．may have been

下列关于OSPF 协议分区的描述中，错误的是

A． OSPF 协议要求当链路状态发生变化时用洪泛法向全网路由器发送此信息

B．OSPF 每个路由器的链路状态数据库包含着本区域的拓扑结构信息

C．每一个区域OSPF 拥有一个32 位的区域标识符

D．OSPF 划分区域能提高路由更新收敛速度