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

Fact 2: Most mammals can be active even in cold weather because they are warm-blooded.

Given the two facts above, answer the question "which can help warm-blooded animals stay active in cold?" with the following options: 
- shivering
 - four limbs
 - Animal fur
 - sleep
 - sweating
 - hibernation
 - cold blood
 - fur seals


 

 shivering        