在【托福阅读那些“已暴露”的出题点】这篇文章中，托福小编已经为大家分析了八个托福考试阅读题目的常见出题点，其中关于“主题段和主题句的关键词”这一出题点：托福文章的主题段和主题句都是参与文章结构搭建的，这些关键词对于理解及把握全文的结构非常重要。所以，文章中有很多的重要信息也会包含在这部分内容中。ETS当然不会放过在这些地方出题。
小编马上用例题解析的方式详细说明。
举例一：来自TPO4 Petroleum Resources--第3题
Paragraph 1: Petroleum, consisting of crude oil and natural gas, seems to originate from organic matter in marine sediment. Microscopic organisms settle to the seafloor and accumulate in marine mud. The organic matter may partially decompose, using up the dissolved oxygen in the sediment. As soon as the oxygen is gone, decay stops and the remaining organic matter is preserved.
Paragraph 2: Continued sedimentation—the process of deposits’ settling on the sea bottom—buries the organic matter and subjects it to higher temperatures and pressures, which convert the organic matter to oil and gas. As muddy sediments are pressed together, the gas and small droplets of oil may be squeezed out of the mud and may move into sandy layers nearby. Over long periods of time (millions of years), accumulations of gas and oil can collect in the sandy layers. Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment.
In paragraphs 1 and 2, the author’s primary purpose is to
○describe how petroleum is formed
○explain why petroleum formation is a slow process
○provide evidence that a marine environment is necessary for petroleum formation
○show that oil commonly occurs in association with gas
答案:A，修辞目的题
解析：本题实际上是在问段落一以及段落二的段落大意。第一段简要说明石油形成，关键词有Petroleum、originate from、 sediment;第二段进一步讲解，都在讲石油形成，关键词有Continued，sedimentation。所以只要找到与“形成”相关的关键词以及有关过程的概念，就容易找到答题方向。
考点：段落大意。
举例二：来自TPO6 Powering the Industrial Revolution—第2题
Paragraph 1: In Britain one of the most dramatic changes of the Industrial Revolution was the harnessing of power. Until the reign of George Ⅲ(1760-1820), available sources of power for work and travel had not increased since the Middle Ages. There were three sources of power: animal or human muscles; the wind, operating on sail or windmill; and running water. Only the last of these was suited at all to the continuous operating of machines, and although waterpower abounded in Lancashire and Scotland and ran grain mills as well as textile mills, it had one great disadvantage: streams flowed where nature intended them to, and water-driven factories had to be located on their banks whether or not the location was desirable for other reasons. Furthermore, even the most reliable waterpower varied with the seasons and disappeared in a drought. The new age of machinery, in short, could not have been born without a new source of both movable and constant power.
Paragraph 2: The source had long been known but not exploited. Early in the eighteenth century, a pump had come into use in which expanding steam raised a piston in a cylinder, and atmospheric pressure brought it down again when the steam condensed inside the cylinder to form a vacuum. This “atmospheric engine,” invented by Thomas Savery and vastly improved by his partner, Thomas Newcomen, embodied revolutionary principles, but it was so slow and wasteful of fuel that it could not be employed outside the coal mines for which it had been designed. In the 1760s, James Watt perfected a separate condenser for the steam, so that the cylinder did not have to be cooled at every stroke; then he devised a way to make the piston turn a wheel and thus convert reciprocating (back and forth) motion into rotary motion. He thereby transformed an inefficient pump of limited use into a steam engine of a thousand uses. The final step came when steam was introduced into the cylinder to drive the piston backward as well as forward, thereby increasing the speed of the engine and cutting its fuel consumption.
Which of the following best describes the relation of paragraph 2 to paragraph 1?
○Paragraph 2 shows how the problem discussed in paragraph 1 arose.
○Paragraph 2 explains how the problem presented in paragraph 1 came to be solved.
○Paragraph 2 provides a more technical discussion of the problem introduced in paragraph 1.
○Paragraph 2 shows why the problem discussed in paragraph 1 was especially important to solve.
答案：B，文章结构题
解析：第一段提出了水动力的局限性，第二段在讲蒸汽机的发明及改良，这些改良是为了新型大机器生产提供动力的解决方案，所以从第一段到第二段是，问题到解决。
考点：段落大意。
举例三：来自TPO2The origins of cetaceans—第9题
Paragraph 5: An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans ("the walking whale that swam") lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus. The fossil luckily includes a good portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea.
Why does the author use the word “luckily” in mentioning that the Ambulocetus natans fossil included hind legs?
○Fossil legs of early whales are a rare find.
○The legs provided important information about the evolution of cetaceans.
○The discovery allowed scientists to reconstruct a complete skeleton of the whale.
○Until that time, only the front legs of early whales had been discovered.
解析：答案是B
The fossil luckily includes a good portion of the hind legs. 之后在讲的都是the legs怎样怎样，得到哪些与现代动物的比较，所以，选B.而且，关于作者目的的题目一定是和主题相关的，或者全文主旨，或者段落主旨。
考点：段落主旨。
以上就是托福小编关于“主题段和主题句的关键词”这一出题点的详细题目举例，希望大家在做题过程中也能多思考、总结，争取在这类出题点上不会丢分。
您还可能关注：
