Which of the following statements correctly describes what happens to the diaphragm during an inhalation, when the lungs inflate?
a. the diaphragm contracts and flattens.
b. the diaphragm expands.
c. the diaphragm only moves during exhale.
d. the diaphragm returns to its resting state.

The correct answer is A. During an inhalation, the diaphragm contracts and flattens.

Explanation:

In inhalation (incorporation of air into the body) the diaphragm muscle and the intercostal muscles contract. The diaphragm descends from its position and the intercostal muscles, as a consequence of the posture they adopt, elevate the ribs. When this happens, the volume of the rib cage increases together with the volume of the lungs, and more space is available. As the volume of the lungs rises, the air pressure in them decreases. Product of the pressure difference (now greater in the exterior) the air penetrates quickly through the respiratory tract to the inside of the lungs.