定語從句是中學(xué)英語語法中的重點(diǎn)內(nèi)容，也是高考中常考查的一個(gè)考點(diǎn)。掌握定語從句的用法，必須突破以下六道難關(guān)：
一、選準(zhǔn)關(guān)系代詞和關(guān)系副詞
在定語從句中，關(guān)系代詞或關(guān)系副詞都代替先行詞在從句中充當(dāng)一定的成分，如果該從句中缺少主語、表語、賓語或定語，就要用關(guān)系代詞來連接從句；如果從句中缺少狀語，就得用關(guān)系副詞來連接從句。例如：
(1)I still remember the days which / that we spent together.
(2)I still remember the days when we worked together.
二、了解僅用that 引導(dǎo)限制性定語從句的幾種情況
that 在限制性定語從句中既可指人又可指事或物。在下列情況下，只能用that 來引導(dǎo)定語從句：
1. 先行詞是all , much, few, little, everything, anything, nothing 等不定代詞時(shí)。例如：
Is there anything that you want to buy?
2. 先行詞被all, few, little, much, every, some, no等詞修飾或被the only, the very, the same, the last 等限定詞修飾時(shí)。例如：
These are all the pictures that I have seen.
This is the very dictionary that is of great help.
3. 先行詞既指人又指物時(shí)。例如：
My father and his teacher talked a lot about the things and the persons that they could remember.
4. 關(guān)系代詞在定語從句中作表語時(shí)。例如：
Our school is not the one that it used to be.
5. 先行詞被形容詞最高級(jí)或序數(shù)詞修飾時(shí)。例如：
This is the best English film that I have ever seen.
The first English novel that I read was A Tale of Two Cities.
6. 主句是who 或which 引導(dǎo)的特殊問句時(shí)。例如：
Who is the girl that is standing under the tree?
Which is the machine that we used last Sunday?
三、把握“介詞＋關(guān)系代詞”結(jié)構(gòu)中介詞的選用
介詞的選擇與主句中先行詞的搭配密切相關(guān)。例如：
That”s the reason for which he was late for school.
This is the book on which I spent 8 yuan.
注意：
1. 定語從句中謂語動(dòng)詞是含有介詞的動(dòng)詞短語時(shí)，介詞應(yīng)放在動(dòng)詞之后，不能拆開放在關(guān)系代詞前。例如：
This is the key which you are looking for.
This is the baby whom you will look after.
2. 該結(jié)構(gòu)中，關(guān)系代詞指人時(shí)用whom，指物時(shí)用which.
四、弄清as 和which 引導(dǎo)的非限制性定語從句指代整體時(shí)的區(qū)別
1. 位置上的區(qū)別：as 引導(dǎo)的非限制性定語從句的位置比較靈活，可以放在主句前，也可以放在主句后，還可插在主句的中間；而which 引導(dǎo)的非限制性定語從句只能放在主句之后。例如：
As is known to us all, the earth turns around the sun.
The earth, as is known to us all, turns around the sun.
The earth turns around the sun, as is known to us all.
The earth turns around the sun, which our parents once told us when we were very young.
2. 詞義與聯(lián)系上的區(qū)別：as 引導(dǎo)的非限制性定語從句與主句之間有著較為密切的上下文聯(lián)系，as 本身含有“正如”之意；而which 引導(dǎo)的非限制性定語從句與主句之間在邏輯意義上近似并列句，which 本身表示“這”或“這一點(diǎn)”之意。例如：
Light travels faster than sound, as we all know.
Jack came late for school, which made his teacher angry.
五、注意定語從句的主謂一致性
關(guān)系代詞在定語從句中作主語時(shí)，從句的謂語必須與先行詞保持人稱和數(shù)的一致。例如：
Tom is one of the boys who are from the USA.
Tom is the only one of the boys who is from the USA.
六、保持主句的完整性并避免從句成分的重疊
1. 在定語從句中，不管出現(xiàn)任何情況，主句的結(jié)構(gòu)必須完整，即主句必須有主語和謂語，缺一不可，否則，整個(gè)主從復(fù)合句就無法成立。試比較：
(1)Is this factory _______ we visited last week?
(2)Is this the factory _______ we visited last week?
A. which B. where C. what D. the one
分析：
第一題缺少表語，只有填D項(xiàng)才能保持主句的完整性，而其他的選項(xiàng)均為干擾項(xiàng)。
第二題主句本身完整，應(yīng)填的關(guān)系代詞在從句中作visited 的賓語，故應(yīng)選A項(xiàng)。
2. 從定語從句中，關(guān)系代詞或關(guān)系副詞已經(jīng)代替先行詞獨(dú)立地或與相應(yīng)的介詞一起在定語從句中充當(dāng)了一定的成分，因此在定語從句中就不能再出現(xiàn)與關(guān)系代(副)詞重疊的成分。例如：
錯(cuò)句：Is this the train that they took it last Sunday?
分析：該題中that 已經(jīng)代替先行詞the train 在定語從句中充當(dāng)及物動(dòng)詞took 的賓語，故重疊出現(xiàn)的賓語it必須刪去。
總之，突破了以上六道難關(guān)，定語從句中的難題便會(huì)迎刃而解。
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