英语定语从句中只用that不用which的情况,和用who不用whom的情况

先说who和whom,这个很好区分．who在定语从句中可作主语和宾语,而whom只能作宾语．
如：She is the girl who often helps the old man.
She is the girl who/whom you were talking to.
只用that不用which的情况
i.先行词是最高级形容词或者它前面有最高级形容词的时候
This is the best that has been used against pollution.
English is the most difficult subject that you will learn during these
years.
ii.先行词是序数词,或者它前面有一个序数词的时候
He is the last person (that) I want to see.
It is the first American movie of this kind that I've ever seen.
iii.主句已有疑问词who或者which的时候
Which is the bike that you lost?
Who is the woman that was praixed at the meeting?
iv.先行词既有人又有物,宜用that
Do you know the things and persons that they are talking about?
The bike and its rider that had run over an old man were taken to the police
station.
v.先行词是all,much,little,something,everything,anything,nothing,
none,the one等不定代词时
You should hand in all that you have.
We haven't got much that we can offer you.
I mean the one that you talked about just now.
vi.先行词前面Only,any,few,little,no,all,one of,the same,the very 等
词修饰的时候
The only thing that we can do is to give you some money.
Li Ming is the only one that wants to be a teacher.
Li Ming is one of the students that want to be teachers in our class.
vii.有两个定语从句,其中一个关系代词已用which,另外一个宜用that.
Edison built up a factory which produced things that had never been seen
before.