定语从句：在复合句中,修饰某一名词或代词的从句叫定语从句。
先行词：被定语从句所修饰的名词或代词叫先行词。定语从句一般放在先行词的后面。
关系词：引导定语从句词叫关系词。关系词分为关系代词和关系副词。
常见的关系代词有that, which, who (宾格whom, 所有格whose)等,关系代词在从句中做主语，宾语或定语；关系副词有where, when, why等，关系副词在从句中做状语。
关系词的作用：1.代替先行词；2.连接先行词和从句；3.作定语从句的句子成分。
二、定语从句的分类
根据定语从句与先行词的关系,定语从句可分为限制性定语从句和非限制性定语从句。
限制性定语从句紧跟先行词,主句与从句不用逗号分开,从句不可省去；
非限制性定语从句主句与从句之间有逗号分开,起补充说明作用,如省去,意思仍完整。
三、关系代词和关系副词的用法
关系代词/关系副词 先行词 关系词在从句中的成分 能否省略
who/that 人 主语 否
who/whom/that/介词+whom 人 宾语 能
whose/of which 人 定语 否
that/which 物 主语 否
that/which/介词+which 物 宾语 能
whose/of which 物 定语 否
when/介词+which 时间 状语 否
where/介词+which 地点 状语 否
why/for which 原因 状语 否
注意:(1)当定语从句中含有介词,介词放在句末时,who, that, which可省略,但介词在关系代词前时,只能用“介词+which/whom”结构。例如:
This is the house in which we lived last year.
Please tell me from whom you borrowed the English novel.
(2)含有介词的固定动词词组中,介词不可前置,只能放在原来的位置上。例如:
This is the person whom you are looking for.
(3)that 作介词的宾语时,介词不能放它的前面,只能放在从句中动词的后面。例如:
The city that she lives in is very far away.
(4)关系词只能用that的情况:
a. 先行词被序数词或形容词最高级所修饰,或本身是序数词或形容词最高级时,只能用that。
He was the first person that passed the exam.
b.先行词是all, any, much, many, everything, anything, none, the one等不定代词时,只能用that。
Is there anything that you want to buy in the shop?
c.先行词被the only, the very, the same, the last, little, few 等词修饰时,只能用that,而不用which。
This is the same bike that I lost.
d. 先行词里同时含有人或物时,只能用that, 而不用which.例如:
I can remember well the persons and some pictures that I saw in the room.???
e.以who或which引导的特殊疑问句,为避免重复,只能用that.例如:
Who is the girl that is crying?
(5)关系词只能用which,而不用that 的情况:
a.先行词为that, those时,用which, 而不用that.例如:
What’s that which is under the desk?
b.关系代词前有介词时,一般用which,而不用that.例如:
This is the room in which he lives.
c.引导非限制性定语从句,用which, 而不用that.例如:
Tom came back, which made us happy.
4.关系副词的用法
(1)when指时间,其先行词表示时间,在句中作时间状语。when相当于“介词+which”。
I’ll never forget the day when / on which we met for the first time.
(2)where指地点,其先行词表示地点,在句中作地点状语。where相当于“介词+which”。
This is the house where / in which he lived ten years ago.
(3)why 指原因,其先行词是原因(reason),起原因状语作用。why相当于“for which”。
There was no reason why/for which she was late again.
5.表示时间、地点的名词后关系词的选用
当先行词是表示时间、地点的名词时，有时用when/?where，有时用that/?which引导定语从句。这时要根据从句的谓语动词是及物的还是不及物的而定。如果是及物动词就用that/?which（作从句的主语或宾语）；如果是不及物动词，就用when/?where（作从句的状语。）
试比较：
This?is?the?house?where?he?lived?last?year.?
This?is?the?house?that/?which?he?visited?last?year.?
I?thought?of?the?happy?days?when I?stayed?in?Beijing.?
I?have?never?forgotten?the?days?that /?which?we?spent?together.?
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