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在这里发现一二两句话题一样，无需讨论，末句话题发生变化，而且在意义上包含了一二句的话题，因为optical computers是fibre optic use的一种用法，分总类型。所以最后该段的主旨定义为fibre optic use方面的发展。
C. But it is not only in technology and commerce that glass has widened its horizons. The use of glass as art, a tradition spins back at least to Roman times, is also booming.…………He now has a new commission - a glass sculpture for the headquarters building of a pizza company - for which his fee is half a million dollars
本段只在第二句话中出现有效话题，那么本段的主题就是本句中的art
D. But not all the glass technology that touches our lives is ultra-modern. Consider the simple light bulb; at the turn of the century most light bulbs were hand blown, and the cost of one was equivalent to half a day’s pay for the average worker…………In this way, the envelope of a light bulb is made by a single machine at the rate of 66,000 an hour, as compared with 1,200 a day produced by a team of four glassblowers.
本段一二句话题出现为由大到小，由泛指到具体，本段主旨可以是泛泛而谈的非ultra-modern科技，也可以是具体的light bulb，通过最后一句没有提到此类科技，所以确定主题为后者。
E. The secret of the versatility of glass lies in its interior structure. Although it is rigid, and thus like a solid, the atoms are arranged in a random disordered fashion, characteristic of a liquid…………..
This looseness in molecular structure gives the material what engineers call tremendous “formability” which allows technicians to tailor glass to whatever they need.
