使用Windows　2000操作系统中，要查看已知文件类型的扩展名，需要在磁盘目录下执行命令(4)设置；用键盘上的Delete　删除软盘中的文件时，该文件(5)；在硬盘上要直接删除文件而不让文件进入回收站，可以用快捷键(6)。

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

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

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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).

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