5.定語從句

定語從句是在句子中起形容詞用途的主謂結構，一般修飾它前面的名詞或代詞，即它的先行詞。定語從句是由關系代詞和關系副詞引導的。

1.關系代詞引導的定語從句

⑴引導定語從句的關系代詞有：who，whom，whose，which，that.

⑵關系代詞在從句作主語、賓語、定語和表語有哪些用途；當作賓語時，關系代詞常常可省略。如：
This is the girl （whom） youve been looking for.

⑶當定語從句所修飾的先行詞是人或人格化的動物時，引導詞用who，whom或whose；

假如先行詞是無生命的東西，用關系代詞which；而that可用于以上兩種狀況。
The man who robbed you has been arrested. That is the book which cosplayt me twenty dollars. Which還可以指嬰兒、動物和表示單數意義的集合名詞，如：
The baby （which） the nurse brought in was Marys child.⑷關系代詞that和which的語法不同當先行詞的前面有形容詞的最高級修飾時，一般用that而不需要which.如：
The final match is one of the most exciting football games that I have ever seen.當定語從句所修飾的先行詞的前面有all，any，little，only，much等修飾時，或者這類先行詞本身就是all，one，little，much，nothing等不定代詞時，一般用that而不需要which. I am interested in all that you have told me. It seems that is the only thing that we can do now.
當定語從句作介詞的賓語時，只能用which而不需要that. The world in which we live is in constant motion and in constant change.當定語從句是與代詞、數詞或名詞詞組連用引導非限定性定語從句時，只能用which而不需要that. I bought a dozen eggs，five of which broke when I dropped the box at my door.
當先行詞的前面有the only （first，last，same，next，very）等詞修飾時，一般用that而不需要which. This is the very movie that I want to see.當被用來指代整個句子，引導非限定性定語從句時，只能用which而不是that. Things then improved，which surprises me. Her brother snatched^{1 the letter away，at which she was furious2.}

2. 關系副詞引導的定語從句

⑴引導定語從句的關系副詞有：when，where，why，how等。

⑵關系副詞when，where，why在從句中作狀語時，可用介詞 which來替代。如：
The reason why （= for which） he is in hospital hasnt been known yet.

3. 限定性定語從句和非限定性定語從句

限定性定語從句與先行詞關系密切，用來描述主句所涉及的人或物的具體狀況，與主句不可分割。這種從句在口語中前后沒停頓，在文字中前后沒逗號。
非限制性定語從句與先行詞之間的關系比較松散，為主句所描繪的人或物提供一些附加狀況，并不是絕對必要。這種從句在口語中有停頓，在文字中總是用逗號與主語隔開。
另外，非限定性定語從句可用which，who，whose，when，where等來引導，但不能用that來引導。如：
The wine，which was in the cellar^{3，was ruined.（非限定性）
The wine which （that） was in the cellar was all ruined.（限定性）
在限定性定語從句中，關系代詞有時可省略；但在非限定性定語從句中，關系代詞不可以省略。}

6.狀語從句

在句子中起狀語用途的句子叫做狀語從句。狀語從句可以坐落于句首、句中或句末。坐落于句首時，從句末一般有逗號與主句隔開；坐落于句中時，從句的前后都需要有逗號；坐落于句末時，從句的前面可以不需要逗號。狀語從句按意義可分為時 間、地址、緣由、條件、讓步、方法、比較、目的和結果等狀語從句。狀語從句由從屬連詞引導。

1.時間狀語從句

引導時間狀語從句的連詞有：after，as，before，once，since，till，until，when，whenever，
now （that），as soon as，as long as，no soonerthan等。
有的名詞短語也可以引導狀語從句，如：
every time，the moment，the instant. When I saw her，she was watching closely at the photo on the wall. As the sun rose，the fog dispersed^{4. The instant he received the letter，he started off at once. Every time he went to Beijing，he used to visit the Great Wall. as，when和while都可以表示主句中動作發生的背景，也可以表示主句的動作與從句的動作同時發生，如：
As he stood there，he heard what they were talking about. I stood up and wanted to go out，when she came in. till和until在主句謂語為持續性動詞的一定式時，作直到為止解，在主句謂語為瞬間動詞的否定式時作直到才解，如：
Lets wait till / until the rain sTOPs. I did not begin work till / until he had gone. once，directly，the moment，the instant和as soon as都作一就解，一般可以互換，如：
once you understand this，you will surely make rapid progress in your study.由副詞加從屬連詞no soonerthan，hardly / barely5 / scarcelywhen等引導的時 間狀語從句，假如no sooner，hardly，barely，scarcely前置句首，主語與謂語須用倒裝結構。如：
Hardly had the film started when they came. No sooner had we reached the TOP of the hill than we all sat down to rest.}