The atmosphere of earth contains primarily which gas?
a.) carbon dioxide
b.) methane
c.) oxygen
d.) nitrogen

well, you see. the answer to your question is quite simple. the thing that is big, powerful, and over 9,000 is your mom.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.