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问题 单项选择题

（）铁素体在室温下溶碳能力很低（只有0.008%），其塑性和韧性好，强度和硬度低，因此，是软韧相，而是硬脆相。

A.渗碳体

B.铁素体

C.低温莱氏体

D.奥氏体

答案

参考答案：A

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. Token Bus

C. Token Ring

D. DQDB
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单项选择题

离心泵启动前泵内未充满水或（）和填料函漏气严重时可造成离心泵启动后不出水或出水量小。

A、吸水管路

B、压水管路

C、配水干管

D、配水支管
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