OSI(Open　System　Interconnection)安全体系方案X.800将安全服务定义为通信开放系统协议层提供的服务，用来保证系统或数据传输有足够的安全性。X.800定义了5类可选的安全服务。下列相关的选项中不属于这5类安全服务的是(63)。

(68)

(66)

Viruses can't be transmitted by(74)and(75)is not a common route for virus infiltration.

(64)

Software refers to(70). The most important software on any computer is(71).

(62)

CPU doesn't mean(68). On a large computer system, a(69)links external devices to a channel.

Modern computers are electronic and(66)devices. The basic building block of a modem computer is a(67).

(60)

(59)