【正文】 defined within the CCITT in 1972. It referred to a network ( ) endtoend digital connectivity ( ) a range of services.a. providing, for b. provision, to c. provided, with d. provide, into答案：a30. Similarly, the introduction of voice encoding techniques ( ) pulse code modulation contributed ( ) the ISDN’s concept evolution.a. usage, on b. using, to c. use, with d. used, so as to答案：b31. The enhanced quality is achieved when a signal is digitally encoded ( ) degradation ( ) the transmission medium.a. overe, to b. overcame, with c. overing, over d. to overe, due to答案：d32. As regards economy, early studies suggested that digital services ( ) significant advantages since a substantial quantity of interface equipment in the telephone exchange could ( ).a. offered, be eliminated b. offer, eliminate c. offers, is eliminated d. to offer, to eliminate答案：d33. As regards economy, early studies suggested that digital services ( ) significant advantages since a substantial quantity of interface equipment in the telephone exchange could ( ).a. offered, be eliminated b. offer, eliminate c. offers, is eliminated d. to offer, to eliminate答案：a34. If we consider binary transmission, the plete information about a particular message will always ( ) by simply ( ) the presence or absence of the pulse.a. obtain, detect b. be obtained, detectingc. obtained, detected d. obtaining, detected答案：b35. An asynchronous serial data link is said ( ) character oriented, as information is transmitted in the form of group of bits ( )characters.a. be, calling b. to being, to call c. been, call d. to be, called答案：d36. It was ( ) in 1969, when the Department of Defense established a nationwide network ( ) a handful of universities and contractors.a. start, connect b. started, to connectc. to start, connected d. to start, to define 答案：b37. Thus was born a new, but perpetually ( ) paging services ( ) at a oneway selective signaling system without speech.a. developing, consisting b. organize, consist ofc. develop, define d. to develop, to define答案：a38. Designers have found it convenient ( ) these nodes into a hierarchy or tree topology, ( ) five classes of switching centers.a. organizing, consisting b. organize, consist ofc. to organize, consisting of d. to organize, to consist of答案：c IV. 根據(jù)句子內(nèi)容選擇正確答案 integrated services digital network is the road map to the future for ( ).A. all forms of data municationsB. all forms of digital munications C. all voice conversationsD. all personal munications答案：B2. The digital service offered the public carriers three very appealing characteristics: ( ) , economy, and flexibility.A. social ability B. great capacity C. high speed D. enhanced quality答案：D3. As regards economy, early studies suggested that digital services offered significant advantages since the substantial quantity of interface equipment in the telephone exchange ( ).A. could be eliminated B. could be used C. could be decreased D. could be widely used答案：A4. Today two 64 kbit/s, or 2Bchannels coupled with a basic access signaling rate of 16 kbit/s, the Dchannel, constitute ( ).A. the information superhighwayB. the local area networkC. the essential ISDN transmission rateD. the synchronous digital hierarchy答案：C5. Currently PSTN offers universal voice access to almost 750 million telephone around the world. ISDN is the network which will provide a similar universal access for ( ).A. voice service as wellB. not only voice but data, video, text, and other services as well C. any analog information including voiceD. high speed data service答案：B6. The public telemunications network can be described ( ).A. using twisted pair of wires B. using many thousands of subscribersC. using four generic architectural ponentsD. using switching nodes答案：C7. The local loop is a pair of wires, generally twisted pair, that ( ).A. connects a subscriber to one of the nodes in the networkB. connects trunk in the networkC. attaches to the toll centerD. attaches to the primary center答案：A8. If the two subscribers are under the aegis of different regional centers, the circuit ( ).A. will involve a digital data systemB. will involve a trunk between regional centersC. will involve a PBX facilityD. will involve many end offices答案：B9. Each subscriber c9onnects via local loop to a switching center, known as ( ).A. a regional center B. a tandem switch C. an end office D. a telephone network答案：C10. There are over 19,000 end offices in the United States, so it is clearly impractical ( ).A. for each end office to have a direct link to each other end officeB. for the US to build so many switching centersC. for each end office to provide video serviceD. for each end office to support many thousands of subscribers答案：A11. With the introduction of digital data system, some subscribers that ( ) have been incorporated into the network.A. can provide video serviceB. transmit broadband programC. contain a transmitter and receiverD. transmit digital signals答案：D12. ( ) , a total path of connected lines is set up from the origin to the destination at the time the call is made, and the path remains allocated to the sourcedestination pair until it is released by the municati