Fact 1: Hibernation is used for conserving energy by some animals.

Fact 2: Energy conservation is an important survival trait.

Given the two facts above, answer the question "What is used as an important survival trait by some animals?" with the following options: 
- bleeding
 - lying
 - hormones
 - food and shelter
 - hibernation
 - four limbs
 - proteins
 - crying


 

     hibernation    