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问题 单项选择题

下面关于UPS开关说法不正确的是（）。

A.主路交流输入开关控制整流器的输入

B.旁路输入开关正常是断开的

C.UPS从正常状态切换到维修旁路是从自动旁路进行过渡的

D.逆变状态时不能合维修旁路开关

答案

参考答案：B

单项选择题

具体判断某一区域水环境污染程度时，位于该区域所有污染源上游、能够提供这一区域水环境本底值的断面称为。（）

A.控制断面

B.对照断面

C.削减断面
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单项选择题

IP multicasting is a set of technologies that enable efficient delivery of data to many locations on a network. Rather than making multiple copies of a message intended to be distributed to multiple recipients at the (71) of origin of a message, multicasting initially sends just one (72) and does not copy it to the individual recipients until it reaches the closest common point on the network, thereby (73) the bandwidth consumed. Network performance is significantly (74) because it isn’t bogged down with the processing and transmission of several large data fries; each receiving computer doesn’t have to (75) the transmitting server for the file.

A．extending

B．minimizing

C．demolishing

D．reducing
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