What happens in the body to trigger the diaphragm to work?

Explanation:

When you breathe in, or inhale, your diaphragm contracts and moves downward. This increases the space in your chest cavity, and your lungs expand into it. The muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.

1. is geographic distribution

2 is increasing complexity

3 is transitional forms