在雅思写作中，一般的简单句会用一个形容词做定语来修饰一个名词，但当定语成分太过复杂而不能只用单个形容词担当时，就要借助于一个句子来做定语修饰名词。
像这样由句子担当定语，对被修饰的先行词进行有限定制约，使该词的含义更具体，更明确，我们称之为限定性定语从句，下面我们结合例句进行对比学习：
a)I don’t like lazy people(形容词做定语放在名词前面).
b)I don’t like the people who never keep their words. 我不喜欢从不遵守诺言的人.
在限定性定语从句中，有两个比较重要的概念。以b句为例,独立主句是：I don’t like the people;定语从句为“who never keep their words”，相当于一个形容词，做定语修饰名词“the people”， 且从句和主句是由who来连接的。在定语从句中，“the people”被称为先行词，指被定语从句所修饰或限制的对象。“who”被称为关系词即重复指代先行词，并在定语从句中充当一定成分的连词。
从上面的解析不难看出，关系词在限定性定语从句中很重要，是连接主句和从句的关键。关系词可以分为关系代词和关系副词，下面我们一起来进行具体的学习。
I.关系代词主要有：who, whom, whose, which, that.
A. 当先行词为人时，可用关系代词who,whom,whose 和that.
a. 若关系代词在从句中做主语时，选用 who 或that.
eg：The woman is a responsible teacher who /that is loved by her students.
= The woman is a responsible teacher and she is loved by her students.
b. 若关系代词在从句中做宾语时，选用 whom(首选),who 或that.
eg: The girl whom we are talking about is a good friend of us.
c. 若关系代词在从句中做定语,表示人的所有关系时，选用 whose 或of whom.
Eg:I know a friend whose sister is a famous dancer.
= I know a friend. His sister is a famous dancer. (whose 代替了his,指人 friend)
B.当先行词为物时，可用关系代词which, that 或whose.
a. 若关系代词在从句中做主语或宾语时，选用 which 或that.
Eg:These are the trees which / that are destroyed in the fire(做主语).
b. 若关系代词在从句中做定语,表示物的所有关系时，选用 whose 或of which.
Eg:The children saw an elephant whose legs were hurt badly.
综上所述，当先行词为人和物时，若在从句中做主语或是宾语，这时可用选用关系代词that，做定语时用whose.
II. 关系副词主要有：where,when 和why.
A. 当先行词为表示地点的名词时，定语从句由副词where引导.
In the sixth century BC, ancient Greece was a country where there were a lot of new ideas.
B. 当先行词为表示时间的名词时，定语从句由副词when引导.
Plato lived at a time when philosophy was very fashionable.
C. 当先行词为表示原因的名词时，定语从句由副词why引导.
Can you tell me the reason why you lied to me?
需要注意的是，限制性定语从句不能被省略，否则句意就不完整，例如I met someone who said he knows you.
通过上面的讲解，同学们在雅思写作过程中对限定性定语从句是否又多了一份了解呢?希望可以有助于您更好的解析英文中的定语从句，从而更好的提高雅思作文中的长难句学习。
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（编辑：秦洁）
