posted by rfvv .
1. This is the desk. That belongs to Bill.
= This is the desk that belongs to Bill.
2. This is the window. Bill broke it yesterday.
= This is the window that Bill broke yesterday.
3. This is the book. Its cover is red.
= This is the book whose cover is red.
4. This is the book. The cover of it is red.
= This is the book the cover of which is red.
= This is the book of which the cover is red.
(Are they all grammatical? Are there any wrong expressions?)
4, for the first one seems iffy. You might wanna use a comma after book.
=This is the book, the cover of which is red.
If you get so desperate just type your sentences in to microsoft word and spell check
The first three sentences are correct.
For number 4, it would be better to say
This is the red book.
This is the book with the red cover.