Fact 1: Mammals breathe with the help of a diaphragm.

Fact 2: Belly breathing uses the diaphragm, which helps relax the lungs.

Given the two facts above, answer the question "What breathes by relaxing the lungs?" with the following options: 
- mammals
 - tortoises
 - dogs
 - chickens
 - ducks
 - humans
 - crocodiles
 - animals


 

 mammals        