In humans and other multicellular organisms, which substance plays a central role as an energy source?
water
fats
O carbohydrates
proteins

Explanation:

Carbohydrates are the main energy source of the human diet. 

Fats are also a source of energy but fats are the slowest source of energy.

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.