当先行词为主句表语或关系代词为从句表语时,只能用that不用which.

其实关于which到底能不能做表语,很多权威语法书都有争议。到目前为止,有一些权威书上写有：先行词在主句中作表语,关系词在从句中作表语时宜用 that 而不用 which 。例如：This isn't the book that I borrowed from the library。属于先行词在主句中作表语。Shenzhen is no longer the city that it used to be。属于引导词在从句中作表语。有争议说 which 可作表语,如,She was fond of dancing,which her brother never was。但只能说明是在非限制性定语从句中,which 可作表语。