单项选择题

Files can be lost or destroyed accidentally. Keep（）copies of all data on removable storage media.

A．backup
B．back　
C．black　
D．backdown

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单项选择题

（）are web sites that search the web for occurrences of a specified word or phrase.

A．Search engines
B．WWW
C．Internet　
D．Java

单项选择题

The（）is a collection of computers connected together by phone lines that allows for the global sharing information.

A．interface　
B．Internet
C．LAN　
D．WWW

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