which在名词性从句的用法：1.宾语从句which是一个连接代词,在宾语从句中可以充当主语，宾语或定语。意思是“哪一个”如：I don't know which bike belongs to my father.I wonder which is better ,this one or that one?He asked me which I liked best. 2.主语从句which 在主语从句中的用法与宾语从句相类似。which boy she likes best is still a mystery.Which students will be sent to take part in the sports meeting hasn't been decided.3.表语从句which 在表语中的用法与主语从句和宾语从句的用法也相似。如：His question is which student is the best at English. The question is which place he wants to go to .4.同位语从句which在同位语从句中的用法不多，只用在某些名词的后面，常见的有idea。I have no idea which picture is the most beautiful of all.顺便讲一下，what引导的名词性从句，也是连接代词，但表示的是泛指的东西；which指的是在一定的范围内，哪一个。