当在there be句型中,通常情况下用that,不用which 原因是什么

你说的是这种情况吧?Is there anything that I can do for you （不用which)
如果是这样,我告诉你,你理解错了.定语从句中只用that,不用which的情况归纳
1） 当先行词是：all ,any ,anything ,everything ,nothing或被它们修饰时.例如：
Is there anything that I can do for you
有什么可以为你做的吗?
All that can be done must be done .
凡是能做的都必须做.
2）当先行词被形容词的*或序数词修饰时.例如：
That is one of the most interesting books that are sold in the bookshop .
那是这家书店出售的最有趣的书之一.
The first thing that we should do is to get some food .
我们该做的第一件事是弄点吃的.
3）当先行词有：the only ,the very ,the same ,the last 等修饰时.例如：
My necklace is not the only thing that's missing .
我的项链不仅是丢掉的东西.
4）当主句以who或which开头时,定语从句中引导词用that ,不用which 或 who .以避免重复.例如：
Who is the girl that is wearing a red coat
正穿一件红色外套的女孩子是谁?
5）当先行词既有人又有物时,用that .例如：
The writer and his novel that you have just talked about are really well known .
你刚才谈起的那位作家以及他的小说确实很著名.