从认证中心CA获取用户B的数字证书，该证书用 (53) 做数字签名；从用户B的数字证书中可以获得 (54) 。

A socket is composed of two addresses: (74) .Heterogeneous network environments consist of computer systems from (75) vendors that run different operating systems and communication protocols.

A．放大
B．调制
C．采样
D．解码

A．3
B．12
C．375
D．100