托福阅读长难句是考生阅读的最大障碍，考生往往看不清楚句子的重点在哪。其实托福阅读长难句一般包括四大类型。考生只要清楚这四种类型的句子结构，并结合相关难句分析练习，就可以对长难句有所把握。前程百利小编为大家带来托福阅读长难句四大类型介绍。
长难句是对应简单句的，它指的是结构复杂、有长度的句子。简单句是只有主谓宾基本结构的句子。长难句一般分为四种，包括有复杂修饰成分、插入语的句子以及倒装句和省略句。复杂修饰常包含状语、定语、宾语、同位语和基础短语修饰等。这只是理想状态下的分类，在实际的句子中，这些类型可能会同时体现在一个句子中，需要考生对句子的分析。
第一种：复杂修饰成分
以TPO Extinction of the Dinosaurs中的句子为例：
Many plants and animals disappear abruptly from the fossil record as one moves from layers of rock documenting the end of the Cretaceous up into rocks representing the beginning of the Cenozoic the era after the Mesozoic.
分析：句子主干是Many plants and animals disappear....句子中的成分as one moves from …up into …属于状语成分。
TPO 3 The Long-Term Stability of Ecosystems中的句子：
Ecologists are especially interested to know what factors contribute to there silience of communities because climax communities all over the world are being severely damaged or destroyed by human activities.
分析：句子主干是Ecologists are interested to know…其中what factors contribute to the resilience of communities是what引导的宾语从句; because climax communities all over the world are being severely damaged or destroyed by human activities是原因状语从句。
第二种：插入语
以TPO3Depletion of the Ogallala Aquifer中的句子为例：
In the early twentieth century, however, it was discovered that much of the High Plains was underlain by a huge aquifer (a rock layer containing large quantities of groundwater).
分析：句子主干是it was discovered that…;其中that much of the High Plains was underlain by a huge aquifer是that引导的主语从句;however是插入语，这个成分在阅读时会使句子被分隔，容易干扰考生阅读的连贯性。
第三种：倒装句
英语句子中的倒装分为部分倒装和完全倒装，部分倒装是指句子中的谓语动词的一部分移到了主语的前面;完全倒装是整个谓语动词都放在主语之前。.
TPO5 Minerals and Plants中的句子：
Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals – an environmentally friendly approach known as phytoremediation.
分析：此句属于部分倒装，其中have considered是整个句子的谓语动词，引起倒装的是have放在了主语investigators之前。
TPO15Glacier Formation中的倒装句：
In contrast, should another ice age occur, sea level would drop drastically. During the last ice age, sea level dropped about 120 meters.
分析：此句属于部分倒装，其中should occur是整个句子的谓语动词，引起倒装的是should放在了主语another ice之前。
再来看OG中的一个句子：
Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.
分析：此句属于完全倒装，其中were missing是整个句子的谓语动词，引起倒装的是谓语放在了主语fossils之前。
第四种：省略句
省略是为了避免重复、突出新信息并使上下文紧密连接的一种手段，英语中省略形式多样，从单词、短语到分句，都可以省略。
TPO25The Evolutionary Origin of Plants中的省略句：
In addition, other lines of evidence support the hypothesis that land plants evolved from ancestral green algae used the same type of chlorophyll and accessory pigments in photosynthesis as do land plants.
分析：句子最后的as do land plants省略了宾语成分，谓语用do代替，正常应该是：land plants used the type of chlorophyll and accessory pigments in photosynthesis…
以上就是前程百利小编为大家带来的托福阅读长难句四大类型介绍，考生在做题以及长难句专项练习时要注意从句子类型出发分析句子，得到最好的句子理解。预祝大家托福考试取得好成绩!
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