Possible answers:
 a). garbage
 b). Generating heat
 c). Space travel
 d). running and lifting
 e). Time and energy
 f). exercise
 g). money
 h). Riding a bike
Given those answer options, answer the question: Fact 1: Playing is one way mammals and other animals learn how to behave.  Fact 2: Involvement in play takes time and energy.  Given the two facts above, what is one way animals learn to behave?
A:
e).