Fact 1: Some animals' fur grows thicker for staying warm in the winter.

Fact 2: Mammals are animals that are born with fur or hair.

Given the two facts above, answer the question "What are born with fur that grows thicker for warmth in winter?" with the following options: 
- bullfrogs
 - insects
 - birds
 - monotremes
 - turtles
 - mammals
 - pigeons
 - Echinoids


 

      mammals   