what 和which 在引导从句时有什么区别?

that,what和which 1.that引导名词性从句时只起连接从句的作用,本身没有任何意义,因此在从句中不充当任何句子成分,它的使用须注意以下几点:A.引导宾语从句时,that常可省略,但如果主句后跟有并列宾语从句时,只能省略第一个that;若宾语从句前插有别的从句时,that也不能省略.例如:He told me (that) he was all right and that he would come to see me when he was free.他告诉我说他很好,并说在他有空时来看我.B.that引导主语从句位于句首时不可省略.如果it作形式主语,而that从句置于句末,这时that可以省略.例如:That he has lost his work is not true.他丢了工作不是真的.=It is not true (that) he has lost his work.C.当主语为the reason时,注意应用that 引导其表语从句,不能受汉语影响而误用because.例如:The reason why he was late was that he missed the early bus.他迟到的原因是他没赶上早班车.(此句中的that不可用because代替) D.引导同位语从句时,切不可错用which.例如:Word has come that some American guests will come to visit our school next week.有消息说下周将有一些美国客人来我校参观.2.what与which引导名词性从句时都在从句中充当句子的某一成份,如主语、表语、宾语或定语,其区别是:what表示泛指的事物,常译为"什么"或"所……的事物",whatever是它的强语势"无论什么";which表示特定事物中的"哪一个(些)",一般情况下在从句中充当定语,后接名词,在一定的语境中,它所修饰的名词可以省略,whichever是它的强语势"无论哪一个(些)".例如:I believe what (whatever) he says.我相信他说的(不管他说什么我都相信).I will give her which (whichever) book she likes on the shelf.这个书架上的(任何一本)书,只要她喜欢,我都会给她.