1 在定语从句中，被修饰的名词或代词称为先行词;引导定语从句的连接词称为关系词, 其中that、which、who称为关系代词,where、when、how,why称为关系副词

2. 关系代词who、whom 和whose指人,分别在从句中作主语、宾语和定语。which指物that多指物, 有时也指人,它们在从句中可以作主语或宾语。

定语从句中关系代词作从句宾语时可以省略。

This is the thief (that/who/whom) we have been looking for these days. (这个就是我们近日一直在找的小偷。)

Please find a room which is big enough for all of us to live in. (请找一间足够大能住下我们全体的房间。)

3. 关系代词as

such  + n + as … the same +n+ as …指物或整个句子.

These houses are sold at such a low price as people expected.

He is not the same man as he was    (像 … 一样的;像 … 之类;和 … 一样)

4. 关系副词。

when或where引导定语从句时,它们在从句中分别作时间状语和地点状语。

This is the room where they had a quarrel a week ago. (这是一个星期前他们吵架的房间。)

I can never forget the day when I first saw you. (我永远不会忘记第一次见到你的日子。)

why 表示原因。在从句中用作原因状语。

The reason why she is absent from school is that she was ill.

how 表示方式。在从句中用作方式状语。