第1个回答 2008-10-19
that→在定语从句中做主语或宾语→用来指人或指物（可以用who, whom, which替换）
※必须用that的7种情况：
⑴先行词是all, everything, nothing, few, little等不定代词时，必须用that引导。
例句：我会告诉你我知道的一切。
I shall tell you everything that I know.
⑵当先行词被序数词或形容词最高级修饰时必须用that引导。
例句：①我不会忘记我学过的第一课。
I can’t∕won’t forget the first lesson that I learned.
②他是我见过的最可恨的人。
He is the most hateful person that I’ve seen.
⑶当先行词被all, every, little, few, no等修饰时，必须用that引导。
例句：我喜欢你给我的所有的书。
I like all the books that you gave me.
⑷当先行词被the only（唯一的）；the very（恰好，正好）；the same（相同的）；the last(最后的)等修饰时，必须用that引导。
例句：你是我唯一喜欢的人。
You’re the only person that I like.
⑸当先行词既有人又有物时，必须用that引导。
例句：我不知道他们正在谈论的人和事。
I don’t know those persons and things that they are talking about.
⑹当that用做关系副词，修饰表示时间的名词时，可以代替when来引导。
例句：我不会忘记我第一次见到你的那一天。
I can’t forget the day that∕when I first met you.
⑺当句子中已有who出现时，必须用that引导。
例句：正在唱歌的那个女孩是谁？
Who is the girl what is singing?
第2个回答 2008-10-19
1 先行词是不定代词或被不定代词修饰，如：
she wrote to me ,telling me everything that he saw on the way to Shanghai
2 先行词是形容词最高级或被形容词最高级修饰，如：this is the best film that i have ever seen
3 先行词被序数词修饰或本身就是序数词，如：
this is the first city that i will visit
4 先行词是物，被the only,the very 修饰时
如：this is the very thing that we can do now
5 先行词既指人也指物
只有这5种，其中第1，2种情况可分成4种
第3个回答 2008-10-20
只能用that作关系代词的情况：
1在不定代词anything, nothing, the one, all, much, any, few, little等作先行词指物时
Is there anything that you don’t understand?
All that glitters is not gold.
2先行词有the only, the very修饰物时
This is the only book that I want.
He is the very person that/who robbed me of my purse on that day.（修饰人不一定）
3先行词为形容词最高级时
This was the most touching movie of this year that made numerous people cry.
4先行词既有人又有物时
For hours we were talking about the people and places that interested us.
5为避免用词的重复
Who is the man that is making a speech to the students?
6先行词前有序数词或the last修饰时
This is the first novel (that) I have read.
Going to the theatre is the last thing (that) I want to do.
7关系代词在定语从句中充当表语的成分
He is not the man that he used to be.本回答被提问者采纳