Fact 1: Thick fur can be used for keeping warm. Fact 2: Mammals have warm blood, and fur or hair, and breathe air. Given the two facts above, what do mammals keep warm with?

Possible answers:
(a). fats
(b). ears
(c). skulls
(d). Limbs
(e). food
(f). tails
(g). tissue
(h). hair
The answer is:
(h).