The ultimate source of energy that drives wind power is

So we want to know what is the ultimate source of energy that drives wind power. The Sun is the ultimate source of energy because it heats up the Earth's atmosphere. Since the hotter air has lesser density, it starts to rise up. As it rises up it starts to cool. And as it gets cooler, it's density again rises and it gets heavier and starts to fall down. This is what we notice as wind. So the correct answer is: the Sun.

Ibelieve the correct answer would be c.