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

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

单项选择题（） is the sending and receiving of the message by computer. It is a fast, low-cost way of communicating worldwide.

A．LAN　
B．Post office
C．E-Mail
D．Interface

单项选择题（）is not a linear structure

A．Graph
B．Queue
C．Stack　
D．1-dimension array

单项选择题（） is permanently stored in the computer and provides a link between the hardware and other programs that run on the PC.

A．Interface　
B．Operating system
C．Internet
D．Application software