Fact 1: Energy is used for heating a building by a heating system. Fact 2: Energy used for heating is the single most commonly used form of energy worldwide. Given the two facts above, what type of energy is produced the most worldwide?

pick from the following.
(a). photons
(b). food
(c). chemicals
(d). our star
(e). Light
(f). Heating
(g). waves
(h). sound
The answer is:
(f).