Which revision best combines these sentences to improve sentence variety and style?
A) made out of oak I built an extra bookcase because I had too many books; now it just needs to be varnished.
B) I built an extra bookcase made out of oak and it just needs to be varnished. I had too many books.
C) I built an extra bookcase made out of oak. It just needs to be varnished as I had too many books.
D) because I had too many books, I built an extra bookcase made out of oak; now it just needs to be varnished.