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问题 选择题

含有多量钙镁离子的水称为硬水．硬水不宜直接作为锅炉用水，若长期使用会产生大量水垢，导致能耗加大，甚至引起锅炉爆炸．用硬水洗衣服时，比较浪费肥皂．水的硬度与所流经地区的岩性关系密切．在其他条件相同的情况下，流经下列哪种岩性地区的水硬度较大 [ ]

A．花岗岩  

B．砂岩

C．石灰岩  

D．片麻岩

答案

答案：C

单项选择题

For each blank, choose the best answer from the four choices and write down on the answer sheet.

(21) is a six bytes OSI layer 2 address which is burned into every networking device that provides its unique identity for point to point communication.

(22) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.

(23) functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.

(24) is the popular LAN developed under the direction of the IEEE802.5.

(25) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.

（24）是（）

A.Ethernet

B.TokenBus

C.TokenRing

D.DQDB
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问答题 简答题

往复泵中填料函的要求是什么？
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