You are presented with the question "What are born with fur that grows thicker for warmth in winter?" and the following answer choices: 
- bullfrogs
 - insects
 - birds
 - monotremes
 - turtles
 - mammals
 - pigeons
 - Echinoids

Now knowing that some animals' fur grows thicker for staying warm in the winter and mammals are animals that are born with fur or hair, choose the best answer.


 

      mammals   