在北京新航道的托福培训教学过程中经常遇到学生对于托福阅读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。