見過that充當先行詞的狀況（高中課文里有個句子：That wasnt a real diamond necklace you borrowed from me.課本注解說，you borrowed from me是定語從句，修飾that)。

不了解which和who能否充當定語從句的先行詞。

Who did he recommended that you thought was not competent for the job?

他推薦了哪個你感覺不勝任工作？

What did he give you that you sold to Tom? 他給你的什么東西你賣給了湯姆？

Which did he give you that you sold to Tom? 他給你的了哪一個你賣給了湯姆？

這都是我一個人寫的句子。我感覺是沒問題的。