以下就以剑桥雅思1 Practice Test 4中的Reading Passage 1(Glass: Capturing the dance of light)为例解释上述有效话题方法怎样进行：
该篇阅读文章A段主题已给出，以下从B段开始分析每段的一二以及末句
B. On the horizon are optical computers. These could store programs and process information by means of light - pulses from tiny lasers - rather than electrons…….... It is the surge in fibre optic use and in liquid crystal displays that has set the U.S. glass industry (a 16 billion dollar business employing some 150,000 workers) to building new plants to meet demand.
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.
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.
F. Today, scientists continue to experiment with new glass mixtures and building designers test their imaginations with applications of special types of glass. A London architect, Mike Davies, sees even more dramatic buildings using molecular chemistry…………Mike Davies’s vision may indeed be on the way to fulfillment.