關(guān)系代詞有who,whose,whom,which,that等,主要用來引導(dǎo)定語從句,它一方面代表定語從句所修飾的那個名詞,另一方面在從句中充當(dāng)一個成分,如主語,賓語,表語,定語等.
1.關(guān)系代詞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(dāng)介詞放在動詞后時,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(guān)系代詞也不能省略.
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 ...as,such...as,as...as,the same...that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(dāng)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(guān)系代詞可省,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(dāng)that在從句中作補(bǔ)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(jié)構(gòu)中出現(xiàn)定語從句,或在定語從句中出現(xiàn)there be 時,用作主語的關(guān)系代詞也可省略.
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(dāng)先行詞是reason,而且定語從句中作原因狀語時,關(guān)系代詞可用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(dāng)先行詞是way,且在定語從句中作方式狀語時,關(guān)系代詞可用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(dāng)關(guān)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(dāng)先行詞是time時,關(guān)系代詞可用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(guān)系代詞作賓語有時也不能省略.
另:關(guān)系代詞that在從句中作賓語或表語時可省略,例如：
I've forgotten much of the Latin I once knew.
我過去懂拉丁語,現(xiàn)在大都忘了.
He's changed.He's not the man he was.
他變化很大,已不是過去的他了.
資料可見:
建議多看看語法書,或者多問問同學(xué)和老師.光看資料是不一定能看懂的,關(guān)于語法的說明往往晦澀難懂,所以問問別人是必要的.