空气动力直径小于（）um的极细微粉尘，是引起尘肺病的主要粉尘。 A.2 B.5 C.

两个数的差是7，设大数为x，那么两个数的积是______．

三机透平的转速是通过（）串级控制的。

A.一段吸入罐压力

B.二段吸入罐压力

C.三段吸入罐压力

D.四段吸入罐压力

填合适的词语。     

建立(     )    访问(     )    欣赏( )     

进入(     )    敞开(     )    保护(     )

从法律渊源的角度来看，属于行政法规的是（）。

A．《旅行社管理条例》

B．《导游人员管理条例》

C．《风景名胜管理条例》

D．《国家旅游局局长令》

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

(1) 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.

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

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

(4) is the popular LAN developed under the direction of the IEEE 802.5.

(5) 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.

4（）

A．Ethernet

B．Token Bus

C．Token Ring

D．DQDB