Pick from: a). layers of fat. b). Ice cubes. c). wishing. d). Depleting energy stores. e). death. f). with their fur. g). raising their temperature. h). by keeping them warm.
Q: Fact 1: Mammals can also generate little bursts of heat by shivering. Fact 2: Shivering costs the bird, however, by depleting energy stores. Given the two facts above, how can mammals generate heat?
A:
d).