Fact 1: Mammals can also generate little bursts of heat by shivering.

Fact 2: Polar bears are mammals.

Given the two facts above, answer the question "What can polar bears do to generate heat?" with the following options: 
- make fire
 - eat ice
 - stay warm
 - nothing
 - fur
 - motors
 - shiver
 - sweating


 

       shiver  