You are presented with the question "What do mammals use to conserve body heat?" and the following answer choices: 
- four limbs
 - Energy.
 - energy
 - sarcasm
 - skin
 - keratin
 - sawdust
 - groceries

Now knowing that mammals conserve body heat with their hair or fur and hair and feathers are both made of keratin, choose the best answer.


 

      keratin   