我們之前講解過，學術英語的長難句很多都是多層次結構的，有主干有分支，分支中還可能有更下一級的分支。今天我們來看看托福官方模擬題第三套TPO 3的一個句子，這個句子解釋了建筑的支撐方法和材料的發展：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.

我們首先積累一下重點生詞：
Employ：v. 采取
Physical law: n. 物理法則
Dramatically: adv. 急劇地
 
我們去掉所有的分支，看看句子的主干，就是 architecture employs methods of support 建筑采取了支撐方式。

分支1 目的狀語：In order for the structure to achieve the size and strength necessary to meet its purpose 這是in order 引導的目的狀語，是主句（建筑采取支持方式）的目的。表示：為了使得建筑結構獲得滿足目的的尺寸和強度。
 
分支2 定語從句：that, because they are based on physical laws, have changed little since people first discovered them—even while building materials have changed dramatically 這里一大長串是 that 引導的定語從句，修飾前面的 methods of support 支持方式。這里的難點是定語從句里面還套著從句，我們要理清這個定語從句的主干和從句！

定語從句的主干是that (指代前文 methods of support) have changed little since people first discovered them  是說 支撐方法自從人們發現它們之后就沒有怎么改變
 
定語從句的分支-原因狀語從句：because they are based on physical laws 因為它們（支撐方法）基于物理法則。這里說明了支撐方法這么久沒有改變的原因。
 
定語從句的分支-讓步狀語從句：even while building materials have changed dramatically 即便建筑材料發生了急劇的改變。這里是做了對比，說明建筑的支撐方法沒有怎么變即便建筑材料發生了大的改變。
 
從句套從句是比較復雜的，這里的定語從句里面還套著2個從句，所以大家一定要理清各個結構啊。