定語從句是中學英語語法中的重點內容，也是大學聯考中常考查的`一個考點。掌握定語從句的用法，必須突破以下六道難關：
一、選準關係代詞和關係副詞
在定語從句中，關係代詞或關係副詞都代替先行詞在從句中充當一定的成分，如果該從句中缺少主語、表語、賓語或定語，就要用關係代詞來連接從句；如果從句中缺少狀語，就得用關係副詞來連接從句。例如：
（1）I still remember the days which / that we spent together.
（2）I still remember the days when we worked together.
二、瞭解僅用that引導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來引導定語從句：
1.先行詞是all , much, few, little, everything, anything, nothing等不定代詞時。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。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。例如：
My father and his teacher talked a lot about the things and the persons that they could remember.
4.關係代詞在定語從句中作表語時。例如：
Our school is not the one that it used to be.
5.先行詞被形容詞最高級或序數詞修飾時。例如：
This is the best English film that I have ever seen.
The first English novel that I read was A 高二 Tale of Two Cities.
6.主句是who或which引導的特殊問句時。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＋關係代詞”結構中介詞的選用
介詞的選擇與主句中先行詞的搭配密切相關。例如：
That is the reason for which he was late for school.
This is the book on which I spent 8 yuan.
注意：
1.定語從句中謂語動詞是含有介詞的動詞短語時，介詞應放在動詞之後，不能拆開放在關係代詞前。例如：
This is the key which you are looking for.
This is the baby whom you will look after.
2.該結構中，關係代詞指人時用whom，指物時用which。
