You are presented with the quiz "What aspect of mammals is especially important in cold climates?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "mammals have a layer of fat under the skin to help insulate the body" and "insulation is very important in a cold climate like Arkhangelsk". 

So, what's the best answer to the question?


 

 layer of body fat under skin          