定語從句which,whom,who,that什麼時候可以省略

定語從句which,whom,who,that可以省略的情況：

1.關係代詞which,whom,who,that在定語從句中作賓語時可以省略.

Here is the man (who/that/whom)you're been looking for.

以下情況不能省略：

（1）在介詞+whom與介詞+which中,whom,which不能省略.

Do you know any shops nearby in which I can buy flowers?

That is the headmaster with whom my father was talking just now.

注：當介詞放在動詞後時,which,whom就可以省略.

Who is the man (whom) you talked with just now?

（2）在非限制性定語從句中,作賓語的關係代詞也不能省略.

Mr Green,whom you know,is the tallest in our school.

The elephant is like a spear,as anybody can see.

（3）在the same ,,,the 中,as,that即使作賓語,也不能省略I have bought the same bicycle as you have (bought). (指同類用as)

This is the same book that I read the day before yesterday. (that指同一個)

（4）當由and,but,or等連詞連接兩個或兩個以上的`定語從句修飾一個先行詞時,第一個關係代詞可省,但第二,第三個不可省略.

This is the book (which) I read yesterday and which I find very interesting.

2.當that在從句中作補語時可以省略.

He is not the man (that) he used to be.

She is all (that) a teacher should be.

3.在there be 結構中出現定語從句,或在定語從句中出現there be 時,用作主語的關係代詞也可省略.

There is a man downstairs (who) wants to see you.

This is the best dictionary (that) there is in the library.

4.狀語的省略

（1）當先行詞是reason,而且定語從句中作原因狀語時,關係代詞可用why,that,也可以省略.

The reason (why/that) he failed was his laziness.

That is the reason (why) I did it.

（2）當先行詞是way,且在定語從句中作方式狀語時,關係代詞可用in which,that,也可以省略.

The way (in which/that) these comrades look at problems is wrong.

That was the way (in which/that) she worked the problem out.

注意：當關系代詞在定語從句中作主語時,不省略.

例如：I don't know the way that/ which leads to the top of the mountains.

(3)當先行詞是time時,關係代詞可用when,that 或省略.

The second time (that) I saw him was in 1980.

I don't know the exact time (when/that) the sports meet will take place.

注意：關係代詞作賓語有時也不能省略.