...不用which?又在什么情况下只用which,不用that呢答:nothing等不定代词,或被first,last,only,few,much,some,no,any以及形容词的最高级修饰时,只能用that,不能用which。如:All (that)they needed were qualified workers.This is the most difficult book (that)I have ever read.(3)在非限制性定语从句中,只能用which,who,as,不能用that。