你說的是這種情況吧?Is there anything that I can do for you （不用which)
如果是這樣,我告訴你,你理解錯了.定語從句中只用that,不用which的情況歸納
1） 當先行詞是：all ,any ,anything ,everything ,nothing或被它們修飾時.例如：
Is there anything that I can do for you
有什么可以為你做的嗎?
All that can be done must be done .
凡是能做的都必須做.
2）當先行詞被形容詞的最高級或序數(shù)詞修飾時.例如：
That is one of the most interesting books that are sold in the bookshop .
那是這家書店出售的最有趣的書之一.
The first thing that we should do is to get some food .
我們該做的第一件事是弄點吃的.
3）當先行詞有：the only ,the very ,the same ,the last 等修飾時.例如：
My necklace is not the only thing that's missing .
我的項鏈不僅是丟掉的東西.
4）當主句以who或which開頭時,定語從句中引導詞用that ,不用which 或 who .以避免重復.例如：
Who is the girl that is wearing a red coat
正穿一件紅色外套的女孩子是誰?
5）當先行詞既有人又有物時,用that .例如：
The writer and his novel that you have just talked about are really well known .
你剛才談起的那位作家以及他的小說確實很著名.