Which revision best combines these sentences to improve sentence variety and style?
a. Made out of oak built an extra bookcase because I had too many books; now it just 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