Birds turn their eggs periodically to:
a. keep them warm
c. them develop properly
b. give them oxygen
d. none of the above

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.