1. 所有關係代詞that，who ，whom， which， whose 引出的定語從句
* 關係代詞修飾先行詞，語法上要充當從句得主語，賓語，定語等。
* 非正式文體中，作賓語得關係代詞常省略；作主語得在句型為：it be……， that be …… ， there be……時才省略。
* 從句的謂語要與修飾語保持一致。
This is the book whiich/that has just appeared.
The girl （whom/that） you saw yesterday is my girlfriend.
Then he met Mary， who nivited him to a party.
Here is Alice， （whom） I mentioned the other day.
* 若先行詞是everything， something， anything， none， one， some， little， much， the only， the very， 最高階等，有人和物組成時，用that或省略；人時用who or whose.
Is that everything that you want to tell us？
This is the only property that i have.
He is the greatest man that has ever lived in that country——這個that作主語在這裡不能省略，請注意！
There are only three boys and two cars that i can see.
2. 關係代詞as ， but 引出的.定語從句
* as 可用在the same……as， such……as， as……as……等結構中，作主語，賓語，表語，狀語等成分。
* but 此時= that/who/which ……not. 與帶有否定詞的主句連用，在從句中一般作主語。
In the nuclear power station we use the same generator as is used in the thermal power station.
Ice consists of the same nolecules as water （consist of）
I have never seen such kind of people as they are.
There is no rule but has （which/that does not have） exception.
3. 由 “介詞＋whom/which" 引出得定語從句
* 非限制性定語從句中，all， nost， some， any， few， both， one 等可與"of + whom/which" 連用，表示部分與整體得關係。
* 有時候也可以用“名詞/代詞＋of + which" 來引導定語從句。
The colleague with whom I am working can speak French.
The colleagur （whom/that） I am working with can speak French.
The car， for which she paid $1，000 for.
The car， （which/that） she paid $1，000 for.
Moleculcs make up matter， the state of which/whose state can be changed.
*修飾way， direction， distance等名詞時，還可以用"that" 來引導，或是省略
That is the way （in which/that） he worked.
The distance （through which/that） light reavels in a second is about 300，000 kilometers.
4.關係副詞when， where， why 引出得定語從句
* when， where 句中作狀語，＝“介詞＋which"
* 修飾reason可用why or for which or that
* 在非正式文體中，when and why 常省略，where 被介詞後置的形式代替。
I do not remember the day （when/on which） he left.
The year （when/in which） I entered the university was 1908.
With TV， we can see things happen almost at the exact moment （when/that/at which） they are happpening.
That is the rason （why/that/for which） she spoke.
5. as， which 引導的特種定語從句
* 在引導非限制性定語從句時，as，which 代表前面整個句子。
* as 可作主語，賓語，作主語時謂語動詞用第三人稱單數，位置不定。
* which 作主語， 同上，引導的從句不可前置。
As was usual at the weekend， the club was almost empty.
As you can see， we have got a problem with the engine.
Metals have many good propertics， as has been stated before.
He missed the train， which annoyed him very much.