Answer the following question given this paragraph: 

Mammals breathe with the help of a diaphragm . This is the large muscle that extends across the bottom of the chest below the lungs. When the diaphragm contracts, it increases the volume of the chest. This decreases pressure on the lungs and allows air to flow in. When the diaphragm relaxes, it decreases the volume of the chest. This increases pressure on the lungs and forces air out.


Q: What is the large muscle that extends across the bottom of the chest below the lungs called?

 Choices:

- uterus

- pectoral

- abdomen

- diaphragm

A:
diaphragm
