You are presented with the question "Why do bears enter a deep sleep?" and the following answer choices: 
- Thyroid-stimulating hormone
 - prolactin release
 - chemical messengers
 - They can't live in the cold
 - To get some rest
 - To conserve energy
 - Endocrine system
 - They don't like the winter

Now knowing that hibernation is used for conserving energy by some animals and when they hibernate, bears enter a deep sleep, choose the best answer.


 

      To conserve energy   