What does Buck often dream of as he sleeps by the campfire?

A. John Thornton

B. Judge Miller's home

C. His fight with Spitz

D. Primitive man

D. Primitive man, because at ages ago we don't know how to cook and how to build a house, which we have in today's world and we are more civilised but at that time we used to live in caves and some time in open places near a fire to keep them warm so the can live and buck was also sleeping near a campfire so it looks like he was dreaming about the primitive man's who live in open near fire to stay warm and cook there prey.