­­­­­­­­­­­­------Is Bob still performing?

------I’m afraid not. He is said        the stage already as he has become an official.

A．to have left

B．to leave

C．to have been left

D．to be left

IP地址用32位二进制数据表示，这个IP地址实际上由网络地址和主机地址两部分组成，其中网络地址标识一个 ( )
A) 网络 B) IP地址 C) 服务器 D) 主机