教学过程中经常遇到学生对于长难句的分析和理解不到位的情况，长难句的分析和理解会影响学生在托福阅读的理解，尤其是在句子简化题。这次题目解析针对于TPO的一个长难句：

　　Sediments are also dropped where a river slows on entering a lake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick.

　　难句类型： 复杂修饰+插入成分

　　本句的主句结构应当是Sediments are also dropped，but will be located inland at some future date; such beds are sometimes thousands of meters thick. 这是一个由分号隔开的并列句，分号前面的句子结构比较复杂，Sediments are also dropped ，后面跟了一个由where引导的状语从句，紧接着这个状语从句又加上了一个插入结构， the deposited sediments are on a lake floor or the seafloor at first， 然后才开始进行转折but will be located inland at some future date， 但是马上又跟上了一个由when 引导的状语从句。分号后面的半句比较简单 such beds are sometimes thousands of meters thick.同学们面对这样的句子一定要先找主干，把状语从句、插入结构纷纷跳过，从纷繁复杂的句子中找出主干来，才能不被ETS出题人改写的句子所迷惑。

　　译文：

　　当河流汇入湖泊和海洋的时候也会有沉淀，这些沉淀最初在湖底或海底，但将来海平面下降或者陆地崛起时，它们就会分布于内陆，通常厚达几千米。

　　意群训练：

　　Sediments are also dropped where a river slows on entering a lake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick.