不可否认，掌握句子结构对于分析长难句十分重要，但是要想彻底明白句子的含义，除了掌握句子结构之外，还要有丰富的词汇量。由于托福阅读文章偏学术性，因此不可避免地会出现一些学术词汇。然而，托福文章所涉及的文章体裁十分广泛，想穷尽所有考试中的学术词汇是不切实际的。我们只需在练习时把遇到的学术词汇进行整理，仅仅以“认识单词”为目标，不求会写、会说，这样来积累一定的学术词汇，以保证考试遇到相关学术词汇时头脑中有一个基本的概念。 长难句之所以看不懂，是因为句子结构分析不清楚。而句子结构分析不清楚，其根本原因就是语法知识掌握得不够牢固。要想把句子结构分析清楚，首先要掌握英语中的五大基本句型。这五种基本句型分别是： 2. 主+谓+宾(例：I ate an apple.) 3. 主+谓+宾+宾补(例：She found the computer useful.) 4. 主+谓+双宾(例：He gave me a book.) 5. 主+系+表(He is a doctor.) 掌握以上这几种基本句型可以帮助你迅速找到句子的主干，而找到句子的主干是分析句子结构的关键。长难句之所以会感觉到难，是因为句子中含有很多修饰性成分，这些修饰性成分往往给考生分析句子结构带来干扰。因此，考生有必要了解常见的修饰性成分都有哪些。 例：This is particularly true for trees in the middle and upper latitudes, which tend to attain greater heights on ridges, whereas in the tropics the trees reach their greater heights in the valley. 这是一个由which引导的定语从句，先行词是前面的trees。 例：David Douglas, Scottish botanical explorer of the 1830s, found a disturbing change (in the animal life)(around the fort)(during the period)(between his first visit in 1825 and his final contact with the fort in 1832.) 在这句话中，括号里的都是介词短语，做修饰成分。in the animal life做定语修饰前面的名词change;around the fort做地点状语修饰谓语动词found，说明发现的地点;during the period和between his first visit in 1825 and his final contact with the fort in 1832做时间状语修饰谓语动词found，说明发现的地点。 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.) 这句话中的过去分词invented by Thomas Savery and vastly improved by his partner做后置定语修饰前面的名词engine。 The growing power of the elite, who controlled the economy, would give them the means to physically coerce people to move to Teotihuacán and serve as additions to the labor force. 以上就是对托福阅读长难句两大基础和复杂修饰成分的具体介绍，大家在补充了这些知识后，相信面对长难句会有更好的表现。