非限定性定语从句只对所修饰成分起补充说明的作用，去掉以后不影响对句子的理解；

Find out the difference between restrictive and non-restrictive attributive clauses and try to summary the structure of non-restrictive attributive 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。

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.

限定性定语从句告诉我们是哪个短裙。

The defining relative clause tells us which skirt.

请记住，限定性定语从句是给句子增加了重要的信息，句子如果没有了定语从句，其意义不同。

Remember that defining relative clauses are used to add important information. The sentence would have a different meaning without the defining relative clause.

非限定性定语从句给句子增加了额外的信息。

Non-defining relative clauses add extra information to sentences.

那位老人有一个在部队工作的儿子。那么，限定性定语从句就要对先行词。

The old man has a son who is in the army .