Question

He's written a book,the name of which I've forgotten.为什么用of

Answer 1

which代替前面提到的那本书,拆成两句看下

He has written a book,

but I've forgotten the name of the book.the book用关系代词which代替掉,介词of一起跟着提前,去引导非限定性定语从句.注意：这个of是从句里本来就应该有的,并不是在什么情况下选用