托福阅读文章有很多主题，其中说明文是一个比较频繁的文章主题。因为说明文大多涉及到大多数考生枯燥的内容，考生通常不喜欢多做练习，所以往往缺乏解决问题的思路。

　　托福阅读说明文的结构解释

　　一般来说，托福阅读中的说明文会表明某种现象。文章的段落是:介绍背景，引出以下内容；未来主段的结构也很清晰:主题句topic sentence   Explain   例如Examples   总结句Summary。事实上，它与我们高考语文有着相似之处。以下是案例分析：

　　官方真题Oficial-19 The Roman Army's Impact on Britain

　　In the wake of the Roman Empire's conquest of Britain in the first century A.D., a large number of troops stayed in the new province, and these troops had a considerable impact on Britain with their camps, fortifications, and participation in the local economy. Assessing the impact of the army on the civilian population starts from the realization that the soldiers were always unevenly distributed across the country. Areas rapidly incorporated into the empire were not long affected by the military. Where the army remained stationed, its presence was much more influential. The imposition of a military base involved the requisition of native lands for both the fort and the territory needed to feed and exercise the soldiers' animals. The imposition of military rule also robbed local leaders of opportunities to participate in local government, so social development was stunted and the seeds of disaffection sown. This then meant that the military had to remain to suppress rebellion and organize government.

　　留下 these troops had a considerable impact on Britain;也就是说，罗马军队对英国有影响。这句话相当于对试题的讨论，解释了文章的整体背景。未来2年～事实上，这四句话解释了前提，并开始具体说明。要估计军队对平民的影响，首先要了解一个事实：士兵不是平均分布的。既然不是平均分布，那一定是多少。因此，第三句话继续说，有些地方士兵很少：很快融入帝国地区；第四句话说，一些地方士兵影响很大：军队驻扎的地区。第五～回到关键点，也就是what，有什么影响:军营先征地；然后会夺走当地领导参与政府的机会；未来，社会发展将受到阻碍，人民将遭到不满和抵制，最终将受到军事镇压。

　　第一段的句子，虽然句子很长，但其实只需要把握结构层次进行分析，就能找到阅读的重点。

　　因此，总共7句段落，分为三个层次，主题句前提表明重点讨论。事实上，段落句已经完成了backgrounddd introduction双重目的：英国被罗马王国吸引士兵的基地/工事以及参与当地经济的影响。

　　Economic exchange was clearly very important as the Roman army brought with it very substantial spending power. …… Such activities had a major effect on the local area, in particular with the construction of infrastructure such as roads, which improved access to remote areas.

　　第二段从一开始就解释了经济交换的影响：强大的购买力和基础设施建设的帮助。

　　Each soldier received his pay, but in regions without a developed economy there was initially little on which it could be spent. …… These settlements acted like small towns, becoming centers for the artisan and trading populations.

　　第三段还是关于经济的:刚来的时候，士兵有钱，没地方花；最后，部队驻扎地变成了一个小镇。

　　The army also provided a mean of personal advancement for auxiliary soldiers recruited from the native peoples, as a man obtained hereditary Roman citizenship on retirement after service in an auxiliary regiment. …… By the later Roman period, frontier garrisons (groups of soldiers) were only rarely transferred, service in units became effectively hereditary, and forts were no longer populated or maintained at full strength.