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

Fact 2: Animals that sleep through the winter are said to hibernate.

Given the two facts above, answer the question "Why do animals sleep through winter?" with the following options: 
- To conserve energy
 - recovery time from fatigue
 - They get bored
 - Endocrine system
 - They only like warmth
 - dormant state
 - To save time
 - hydration


 

 To conserve energy        