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限制性和非限制性定語從句
例如：
1)This is the house which we bought last month.（限制性)
The house,which we bought last month,is very nice.（非限制性)
2)當先行詞是專有名詞或物主代詞和指示代詞所修飾時，其后的定語從句通常是非限制性的，例如：
Charles Smith,who was my former teacher,retired last year.
My house,which I bought last year,has got a lovely garden.
This novel,which I have read three times,is very touching.
3)非限制性定語從句還能將整個主句作為先行詞,對其進行修飾,這時從句謂語動詞要用第三人稱單數(shù)，例如：
He seems not to have grasped what I meant,which greatly upsets me.
Liquid water changes to vapor,which is called evaporation.
說明：關(guān)系代詞that和關(guān)系副詞why不能引導非限制性定語從句。
