对一路信号进行FSK调制时，若载波频率为fc，调制后的信号频率分别为f1和f2(f1＜f2)，则三者的关系是(16)。当对多路信号进行调制时，调制后各信号的频谱(17)。信号到达接收端后通过(18)分离各路信号。WDM与FDM工作方式相似，但WDM调制的是(19)。ILD是(20)使用的设备。

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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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