4、限制性和非限制性定語(yǔ)從句

1) 定語(yǔ)從句有限制性和非限制性兩種。限制性定語(yǔ)從句是先行詞不可缺少的部分，去掉它主句意思往往不明確；非限制性定語(yǔ)從句是先行詞的附加說(shuō)明，去掉了也不會(huì)影響主句的意思，它與主句之間通常用逗號(hào)分開(kāi)，例如：

This is the house which we bought last month. 這是我們上個(gè)月買(mǎi)的那幢房子。（限制性）

The house, which we bought last month, is very nice.這幢房子很漂亮，是我們上個(gè)月買(mǎi)的。（非限制性）

2) 當(dāng)先行詞是專有名詞或物主代詞和指示代詞所修飾時(shí)，其后的定語(yǔ)從句通常是非限制性的，例如：

Charles Smith, who was my former teacher, retired last year. 查理•史密斯去年退休了，他曾經(jīng)是我的老師。
My house, which I bought last year, has got a lovely garden. 我去年買(mǎi)的的那幢房子帶著個(gè)漂亮的花園。
This novel, which I have read three times, is very touching. 這本小說(shuō)很動(dòng)人，我已經(jīng)讀了三遍。

3) 非限制性定語(yǔ)從句還能將整個(gè)主句作為先行詞, 對(duì)其進(jìn)行修飾, 這時(shí)從句謂語(yǔ)動(dòng)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. 他似乎沒(méi)抓住我的意思，這使我心煩。
Liquid water changes to vapor, which is called evaporation. 液態(tài)水變?yōu)檎羝�，這就叫做蒸發(fā)。

說(shuō)明：關(guān)系代詞that和關(guān)系副詞why不能引導(dǎo)非限制性定語(yǔ)從句。

5、介詞+關(guān)系詞

1）介詞后面的關(guān)系詞不能省略。

2）that前不能有介詞。

3） 某些在從句中充當(dāng)時(shí)間，地點(diǎn)或原因狀語(yǔ)的"介詞+關(guān)系詞"結(jié)構(gòu)可以同關(guān)系副詞when 和where 互換。

This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?