what,that的区别和用法,最好有例句,谢了

当what和that都作关系代词时
what引导名词性从句,that可引导名词性从句,也可引导定语从句,可引导强调句.
1.当what引导名词性从句时
e.g.What he said was true.what从句作整个句子的主语,从句的宾语.
I can't imagine what he has done.what从句作整个句子的宾语,从句的宾语.
It is what is right.what从句作整个句子的表语,从句的主语.
2.当that引导名词性从句时
e.g.That he was admitted to the Fudan university was known.
这里注意的是That后跟一个完整的句子,句子充当一个名词性主语,That从句用法和一一样
3.当that引导定语从句时
e.g.He is a person that/who always helps others.
The title which /that is on the right should be revised.
此处我只举了定语从句的一个方面
4.当that引导强调句时
e.g.It is he that got the straight A's
强调句的特点是把It is和that去掉也能成句