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.