You are presented with the question "What can be used for keeping warm?" and the following answer choices: 
- keratin
 - vacuum
 - four limbs
 - energy
 - cold
 - engines
 - magic
 - heat

Now knowing that thick fur can be used for keeping warm and carpet beetle larvae feed on the keratin and chitin commonly found in wool, fur, or feathers, choose the best answer.


 

 keratin        