一个单位要在4个子网上使用专有的网络号192.168.90.0。在每个子网上最多配备27台主机，该单位应该使用的子网掩码是(25)。

(75)is a mechanism used for protecting the users outside of network from accessing some non-authorized computer resources.

In C language, it is convenient to use a(74)to exit from a loop.

Every host and router on the Internet has an IP address, which encodes its(72).

When you choose a command name that is followed by "..." on menu, a(73)box appears in which you provide more information.

(80)

There are many page replacement algorithms in the page management. Most frequently used algorithm is(71).

缓冲技术中的缓冲池在(60)中，引入缓冲的主要目的是(61)。

(78)

类库是一种事先定义好的程序库，它以程序模块的形式，按照(56)把一组类的定义和实现组织在一起。(57)对类库的建立提供了强有力的支持。

结构化分析方法(SA)是一种预先严格定义需求的方法，强调分析对象的(51)。其指导思想是(52)。