定語從句是在復合句中起定語作用，修飾名詞、代詞或整個主句的從句。被定語從句修飾的詞叫先行詞。引導定語從句的關系詞有關系代詞(that, which, who, whom, whose)和關系副詞（where, when, why等）。
關系代詞在定語從句中的作用：1. 連接主句和定語從句；2. 指代先行詞；3. 在定語從句中充當一定的成分（主語、表語、賓語、定語等）。
The girl who / that is singing is my sister. (作主語，指人)
Luckily, my friend didn’t take the bus that / which had an accident. (作主語，指物)
The teacher (whom / that / who) they are talking with is very friendly. (作賓語，指人)
Soon I received the clothes (that / which) my mother bought for me. (作賓語，指物)
The first English novel that I read was Cities.
This is the most exciting football game that I have ever seen.
?、?先行詞為all, everything, anything, nothing, little, few, much, none, the one等不定代詞時。如： Is there anything that I can do for you?
?、?先行詞被all, any, every, few, little, no, some等詞修飾時。如：
You can take any seat that is free.
?、?先行詞被the only, the very, the last等修飾時。如：
This is the only thing that we can do now.
The boy and the dog that are in the picture are very lovely.
Which is the car that has taken us there?
The house in which we live is very large.
This is the book of which the teacher is speaking.
That which is well done is twice done.
The girl who gives me the pen is my best friend.
The girl (whom) I gave the pen to is my best friend.
The boys whose names were called stood up.
I’d like a room whose window is clean and large.
用適當的關系代詞（that, which, who, whom, whose）填空。
1. You’ll find taxis waiting at the bus station_______________ you can take to reach your family.
2. The old town has narrow streets and small houses_______________ are built close to each other.
3. I’ve become good friends with several of the students in my school _______________ I met in the English speech contest last year.
4. I think this is the most beautiful place ______________I have ever visited.
5. In China, the number of cities is increasing _________development is recognized across the world.
6. This is the very house _______________ we visited last year.
7. The girl _______________ father works in a hospital wants to be a doctor in the future.
8. He visited the teachers and the school _____________ he remembered.
9. The clock is that _______________ can tell us the time.
10. The thought of going back home was all_______________ kept him happy while he was working there.