The other kind of relative clause is called a nonrestrictive or nonessential or non-defining clause.

另种关系句称为非限制性或非必要或非定义性句。

This sort of nonrestrictive clause typically begins with the word " which" .

这种非限制性句通常以单词“which”开头。

If you are writing English, if you use the nonrestrictive clause, the clause that begins typically with " which, " you will usually see a comma (, )before the word " which" .

如果你正英语， 如果你使用非限制性句，通常以“which” 开头的句， 你通常会“which” 词之前看到个逗号 (, )。