--- Hello! Is that Tom over there? Long time no see. Let’s say hello to him.

---Please _____ in the library.

A．keep clean

B．keep quiet

C．wait in line

D．drop litter there

PKI支持的服务不包括（）。

A.非对称密钥技术及证书管理

B.目录服务

C.对称密钥的产生和分发

D.访问控制服务