Relative clauses add extra information to a sentence by defining a noun. They are usually divided into two types –defining relative clauses and non-defining relative clauses.
定语从句是对句子里的名词加入额外的信息。一般来讲,有两种类型的定语从句—限定性定语从句和非限定性定语从句。

Defining relative clauses
限定性定语从句

Look at this sentence:
看如下例句:
The woman who lives next door works in a bank.
‘who lives next door’ is a defining relative clause. It tells us which woman we are talking about.
‘who lives next door’就是限定性定语从句,它告诉我们我们正在谈论的那个“女人”的更多信息。
Look at some more examples:
看看更多的例句:
Look out! There’s the dog that bit my brother.
• The film that we saw last week was awful.
• This is the skirt I bought in the sales.

Can you identify the defining relative clauses? They tell us which dog, which film and which skirt we are talking about.
你能认出上面句子中的限定性定语从句吗?

Relative pronouns
关系代词

Relative clauses are often introduced by a relative pronoun (usually who, which, that, but when, where and whose are also possible)
定语从句经常由关系代词连接(一般是who, which, that, 不过when, where 和whose也是可能的)
With defining relative clauses we can use who or that to talk about people.
在限定性定语从句里,我们能用who和that来指代和谈论别人。
• She’s the woman who cuts my hair.
• She’s the woman that cuts my hair.

And we can use that or which to talk about things.
然后,我们用that和which来指代和谈论事物。
• The dog that bit my brother.
• The dog which bit my brother.

It is also sometimes possible to omit the relative pronoun.
有时候,也可以省略关系代词。
This is the skirt that I bought in the sales.
• This is the skirt which I bought in the sales.
• This is the skirt I bought in the sales.

In this sentence ‘skirt’ is the object of the verb (buy). ‘I’ is the subject. When the relative pronoun is the object, it can be omitted.
在句子中,skirt是动词buy的宾语,而I 是主语,当关系代词是宾语的时候,它可以被省略。
The film we saw last week was awful.
• BUT The dog bit my brother. This is not possible because the dog is the subject of the verb, ‘bite’.