The girl which is reading a book under the tree is my sister.这句知错在哪儿

问题描述:

The girl which is reading a book under the tree is my sister.这句知错在哪儿
是否语法错误

which改为who.
在定语从句中,主句主语是人的话,对主句主语的先行词要用who,而不是which.