Organisms That Maintain a Constant Body Temperature Rely on the Heat

Organisms that maintain a constant body temperature rely on the heat produced by cells.Where does this heat come from?

A) Cells have special metabolic pathways that are exclusively for the production of heat.
B) Mitochondria produce heat in the form of ATP.
C) Plants store heat as they perform photosynthesis; when an organism digests a plant, that heat is released.
D) Heat is a natural by-product of most chemical reactions.