定语从句先行项是什么，只能用that连接？

限制性定语从句中只能用that 引导定语从句的情况

1．当先行词是everything, anything, nothing (something 除外), all, none, few, little, some等代词时，或当先行词受every, any, all, some, no, little, few, much等代词修饰时。如：
Have you taken down everything that Mr. Li said? 李老师讲的你都记下来了吗？
There seems to be nothing that is impossible to him in the world. 对他来说似乎世界上没有什么不可能的事。
All that can be done has been done. 所有能做的都做好了。
There is little that I can do for you. 我不能为你干什么。
He stayed in the library and looked up any information that they needed. 他呆在图书馆查找所需的资料。
注意：当先行词指人时，偶尔也可用关系代词who，如：
Any man that / who has a sense of duty won’t do such a thing. 任何有责任感的人都不会做这样的事。
All the guests that / who were invited to her wedding were important people. 所有应邀来参加她婚礼的客人都是重要人物。
2．当先行词被序数词修饰时。如：
The first place that they visited in London was the Big Ben. 在伦敦他们参观的第一个地方是大本钟。
3．当先行词被形容词最高级修饰时。如：
This is the best film that I have ever seen. 这是我看过的最好的电影。
4．当先行词被the very, the only修饰时。如：