怎样区别most of which和most of them 的用法,请举例说明,

你学过定语从句吧。给你三句话：1 i have many friends which come from china。2 i have many friends,most of which come from china。3 i have many friends。Most of them come from china。Most of which其实是对which加以限定,还是从句。
再问： 可以说most of them是表示两句话，而most of which也是一个非限制性定语从句吗？
再答： 嗯嗯