Answer the following question: You are presented with the question "What keeps mammals warm?" and the following answer choices:  - evaporation  - Animal fur  - staying warm  - sweating  - They have thick fur  - with their fur  - a layer of fat  - Veins and arteries.  Now knowing that mammals have a layer of fat under the skin to help insulate the body and glass insulation keeps beverage warm for hours, choose the best answer.
Answer:
a layer of fat