1 The book which is on the book is mine (在这里,which是从句部分的主语)
====The book is on the desk.The book is mine-------合并：The book (the book==which) is on the desk is mine.
2 The building the windows of which are bright is our shool.（of which ==of the building-----做定语,这房子的- - - - - ）
变成两句就是：The building is our school.The windows of the building are bright.再合并起来：The building the windows of which （of which==of the building）are bright is our shool
==The building of which the windows are bright is our shool.(注意位置的改变)
==The building whose windows are bright is our shool.（注意单词的改换）