The large balloon on the bottom of the bottle represents a diaphragm, whereas the smaller balloons represent a pair of lungs. To represent lung function, Danica gently moves the large balloon that is stretched across the bottom of the bottle up and down. As she pulls the large balloon down, the two small balloons inflate. As she pushes the large balloon up, the two small balloons deflate.

Based on her model, Danica can conclude that
A.
lungs are not connected to any other organs in the human body.
B.
when air enters the lungs, they expand; when air exits the lungs, they shrink.
C.
when air enters the lungs, they shrink; when air exits the lungs, they expand.
D.
lungs are hard, brittle organs that are incapable of expansion.