阅读下面的短文，文中有15处空白，每处空白给出4个选项，请根据短文的内容从4个选项中选择1个最佳答案。 One of the most important technological developments during the 1980s has been the emergence of optical fiber communication as a major international industry. One indication of the (51) of this development is the total (52) of installed fiber, which was estimated to be 3.2 million kilometers in the U.S. alone by the end of 1987. Over 90% of this fiber was placed. (53) during the time period of 1982—1987. Long-haul trunk installations(长途干线设施) have dominated, (54) for about 95% of the fiber in the U.S. In the early 1950s the researchers who produced the first clad glass optical fibers were not (55) of using them. for communications. (56) , fiber optics was already a well-established commercial technology when the famous paper by Kao and Hockham, (57) the use of low-loss optical fibers for communication, appeared in 1966. The first low-loss silica fiber was described in a publication which appeared in October of 1970. The date of this publication is sometimes (58) as the beginning of the era of fiber communication. Although this development did receive (59) attention in the research community at- the time, it was far from inevitable that a major industry would evolve. The technological barriers appeared (60) because there were serious doubts as to (61) these fiber components could ever be produced economically enough, but the market potential was very significant. (62) , research and development activity expanded rapidly, and a number of important issues were (63) during the early 1970s. During the middle and late 1970s, the rate of progress towards marketable products accelerated as the emphasis (64) from research to engineering. Fibers with losses approaching the Payleigh limit of 2 dB/km at a wavelength of 0.8um were produced. By 1980 improvement in component performance, cost, and reliability led to major commitments (65) the part of telephone companies.

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