如果把托福的文章比喻成一座建筑物，“词汇”便是“砖块”，“句子”便是“梁柱”。对于一座建筑物而言少了一两块砖块并不会造成其倒塌，那么对于一篇文章而言某些单词没看懂也并不影响对于整个篇章的理解；而作为建筑物的支撑部分，梁柱却会影响该建筑物的稳定性，那么被比作梁柱的句子对于理解一篇文章而言是至关重要的，无法理解长难句会让考生首先降低阅读速度，其次影响篇章理解，最后最致命的影响是相关题型的解决----“句子简化题”，“事实信息题”，“推理题”，因为这三种题型都是在直接或间接地考察学生对于长难句的理解能力。本文将从这三种题型的角度讨论如何解读长难句。
“句子简化题”中的长难句----“先见森林，后见树木”
“森林”代表的是该句话的“结构”，“先见森林”即考生首先应该关注的是该句话最核心的主干；“树木”代表的是该句话具体的“词汇”，那么“后见树木”指考生应该在了解主干之后才关注词汇，并且只是一些key words.
<1> 因果结构
例题1 (OG: Desert Formation)：
The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of reversing or even slowing the process.
10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. Desertification is a significant problem because it is so hard to reverse and affects large areas of land and great numbers of people.
B. Slowing down the process of desertification is difficult because of population growth that has spread over large areas of land.
C. The spread of deserts is considered a very serious problem that can be solved only if large numbers of people in various countries are involved in the effort.
D. Desertification is extremely hard to reverse unless the population is reduced in the vast areas affected.
解题步骤：
1. 观察题干，发现表示隐形因果的短语result from
2. 浏览选项，发现A和B选项含有因果关系
3. 分析原句：原句中“因”：1). 大量受到影响的土地vast areas of land; 2). 大量受到影响的人口tremendous numbers of people; 3). 很难去减慢或者颠覆沙漠化过程reverse or slow the process; 原句中“果”：沙漠化是一个严重serious的问题；分析A选项：“因”：1). reverse process; 2). affect large areas of land; 3). affect great numbers of people; “果”：沙漠化是一个significant的问题
<2> 让步转折结构
例题2 (TPO 17: Animal Signals in the Rain Forest)：
In the green-to yellow lighting conditions of the lowest levels of the forest, yellow and green would be the brightest colors, but when an animal is signaling, these colors would not be very visible if the animal was sitting in an area with a yellowish or greenish background.
7. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. When an animal is signaling in an area with green-to yellow lighting condition, its signal will not be visible if the background is brightly lit.
B. In the lowest levels of the forest, an animal''s signals are not easily seen unless there is a yellowish or greenish background.
C. In the green-to-yellow lighting conditions at the lowest levels of the forest, only signals that are themselves green or yellow will be bright enough to be seen in most areas.
D. Although green and yellow would be the brightest colors near the forest floor, these colors would make poor signals whenever the forest background was also in the green-to-yellow range.
解题步骤：
1. 分析题干，发现表转折的逻辑关系词but; 前半句“yellow and green会是最亮的颜色在低层森林中”；后半句“但是如果动物所处的background是yellow or greenish, 那么动物发出该种颜色的信号将不明显”
2. 分析选项：只有D选项含有表让步转折的逻辑词although, 进而分析句意：前半句：“虽然green and yellow在森林底层颜色最亮”；后半句：“在环境也是green to yellow的情况下，这些颜色将是poor signals”
3. 原句与选项在句子的结构上符合：转折结构；在语义上符合：lowest level of the forest = forest floor, Not very visible = poor signals
<3> 比较结构
例题3 (TPO 17: Animal Signals in the Rain Forest)：
In the second case, pollinators (insects, birds) obtain food from the flowering plant, and the plant has its pollen distributed and seeds dispersed much more efficiently than they would be if they were carried by the wind only.
9. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. The relationship between flowering plants and pollinators provides pollinators with food and flowers
