Are d orbitals included in hybrid orbitals?

Answer 1

According to Linus Pauling and this reference, the answer is "sometimes"

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch8/hybrid.html

I once audited a course taught by Pauling at Caltech. I also bought his famous book "The Nature of The Chemical Bond". I didn't get far in either. It was all Greek to me.