绞线由两根互相绝缘绞合成螺纹状的导线组成。下面关于双绞线的叙述中，正确的是(3)。  1．它既可以传输模拟信号，也可以传输数字信号  2．安装方便，价格便宜  3．易受外部干扰，误码率低  4．通常只用作建筑物内的局部网通信介质

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Multipurpose Internet Mail Extension(MIME)is a(71)document messaging standard in the Internet enviroment, with MIME, users can send(72)Email messages that include audio, video, graphices, and text to any other user of a TCP/IP network. Richtext information can also be(73)into messages. It defines the fonts, formats, and(74)features of a document so the document can be easily(75)on many different types of systems.

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

(66)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.

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

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

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

(70)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.

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