定语从句进阶：介词+关系代词与as的用法
一、知识点讲解
1. 「介词 + 关系代词」结构
当先行词在定语从句中作介词的宾语时，介词可以提前到关系代词之前，构成「介词 + which/whom」结构：指物用 which，指人用 whom，不能用 that 或 who。介词的选择主要看三点：一是从句中动词与介词的固定搭配，二是先行词与介词的搭配习惯，三是介词短语在句中的整体意义。
例句： - This is the house in which I lived ten years ago.（live in the house） - The man with whom you talked just now is my uncle.（talk with the man） - The pencil with which he wrote was broken.（write with the pencil）
注意：当介词与动词构成不可拆分的固定短语时（如 look after、listen to、depend on），介词必须留在动词之后，不能提前。例如：The babies whom the nurse is looking after are all healthy. 不能说 after whom。
2. as 引导的定语从句
as 可以作关系代词引导定语从句，主要有三种模式： - such ... as：Such books as you like are very popular.（as 在从句中作 like 的宾语） - the same ... as：He made the same mistake as I did.（表示「和……一样的」） - as 引导非限制性定语从句，可置于主句之前、之中或之后，指代整个主句：As we all know, the earth goes around the sun.
二、as 与 which 用法对比
| 比较项 | as | which |
|---|---|---|
| 位置 | 可置于主句前、中、后 | 只能置于主句之后 |
| 语义 | 强调「正如、正像」 | 指代前文所述事实 |
| 固定搭配 | such...as、the same...as | 无固定搭配 |
| 先行词 | 整个主句或某个名词 | 整个主句或某个名词 |
对比例句： - As is known to all, Taiwan is an inalienable part of China.（正如大家所知） - He failed the exam again, which made his parents very angry.（指代前面整件事）
判断口诀：句首只用 as；「正如」必用 as；such/the same 后面跟 as。
三、例题精讲
【例1】The reason ______ he was late for school was that he got up late. A. why B. for which C. that D. A and B
解析：先行词是 reason，从句中缺原因状语，可用 why 或 for which 引导。答案：D。
【例2】He has three good friends, ______ are engineers. A. most of whom B. most of them C. most of which D. most who
解析：非限制性定语从句中「most of + 关系代词」指人用 whom，且先行词 friends 作 of 的宾语。答案：A。
【例3】______ was expected, he passed the driving test at the first attempt. A. Which B. As C. That D. It
解析：从句位于主句之前且表示「正如所料」，用 as 引导非限制性定语从句。答案：B。
四、课后练习
基础题：用适当的关系代词填空。 1. The house __ windows face south is my home.（提示：指物的所属关系） 2. This is the pen ____ which I wrote the letter.
提高题：The teacher ______ whom you should listen is standing over there.（填介词）
挑战题：用 as 引导的定语从句翻译「众所周知，勤奋是成功的关键」，并把「他犯了和我一样的错误」翻译成英文。