Originally introduced by Netscape Communications, (21) are a general mechanism which HTTP Server side applications, such as CGI (22) , can use to both store and retrieve information on the HTTP (23) side of the connection. Basically, Cookies can be used to compensate for the (24) nature of HTTP. The addition of a simple, persistent, client-side state significantly extends the capabilities of WWW-based (25) .

A．fixed

B．flexible

C．stable

D．stateless

对数据库的保护通过（）实现。

A.并发控制

B.数据库的恢复

C.安全性控制

D.完整性控制

E.查询控制