Mammals have a layer of fat under the skin to help insulate the body, and glass insulation keeps beverage warm for hours. Given these facts, what keeps mammals warm among the following options:
- evaporation
 - Animal fur
 - staying warm
 - sweating
 - They have thick fur
 - with their fur
 - a layer of fat
 - Veins and arteries.


 

       a layer of fat  