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问题 选择题

有A、B、C三个用丝线悬吊着的小球，相互作用情况如图：那么下列说法正确的是（　　）

A．若A带正电，则C一定带正电

B．若A带负电，则C一定带正电

C．若B带正电，则A一定带正电，C一定带负电

D．A，B一定带同种电荷，C则可能不带电

答案

答案：D

单项选择题

CREATE DATABASE命令用来建立( )。

A．数据库

B．关系

C．表

D．数据文件
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单项选择题

Frame Relay is simplified form of (51) , similar in principle to (52) , in which synchronous, frames of data are routed to different destinations depending on header information.

Packets are routed throught one or more Virtual Circuits known as (53) . Most Virtual Circuits are (54) , which means that the network provider sets up all DLCI connections at subscription time. (55) are also part of the Frame Relay specification. They privide a link that only lasts only as long as the session.

（52）是（）

A.X.21

B.X.25

C.X.28

D.X.29
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