我们之前讲解过，学术英语的长难句很多都是多层次结构的，有主干有分支，分支中还可能有更下一级的分支。今天我们来看看托福官方模拟题第三套TPO 3的一个句子，这个句子解释了建筑的支撑方法和材料的发展：In order for the structure to achieve the size and strength necessary to meet its purpose, architecture employs methods of support that, because they are based on physical laws, have changed little since people first discovered them—even while building materials have changed dramatically.

我们首先积累一下重点生词：
Employ：v. 采取
Physical law: n. 物理法则
Dramatically: adv. 急剧地
 
我们去掉所有的分支，看看句子的主干，就是 architecture employs methods of support 建筑采取了支撑方式。

分支1 目的状语：In order for the structure to achieve the size and strength necessary to meet its purpose 这是in order 引导的目的状语，是主句（建筑采取支持方式）的目的。表示：为了使得建筑结构获得满足目的的尺寸和强度。
 
分支2 定语从句：that, because they are based on physical laws, have changed little since people first discovered them—even while building materials have changed dramatically 这里一大长串是 that 引导的定语从句，修饰前面的 methods of support 支持方式。这里的难点是定语从句里面还套着从句，我们要理清这个定语从句的主干和从句！

定语从句的主干是that (指代前文 methods of support) have changed little since people first discovered them  是说 支撑方法自从人们发现它们之后就没有怎么改变
 
定语从句的分支-原因状语从句：because they are based on physical laws 因为它们（支撑方法）基于物理法则。这里说明了支撑方法这么久没有改变的原因。
 
定语从句的分支-让步状语从句：even while building materials have changed dramatically 即便建筑材料发生了急剧的改变。这里是做了对比，说明建筑的支撑方法没有怎么变即便建筑材料发生了大的改变。
 
从句套从句是比较复杂的，这里的定语从句里面还套着2个从句，所以大家一定要理清各个结构啊。