You are presented with the question "How do polar bears stay warm in the winter?" and the following answer choices: 
- They have cold blood
 - protect them
 - They eat a lot
 - hard outer covering
 - by indirect light
 - They go swimming
 - They have thick fur
 - When it's cold

Now knowing that some animals' fur grows thicker for staying warm in the winter and polar bears grow fur to survive in the cold, choose the best answer.


 

       They have thick fur  