Air Moves into the Lungs During Inspiration

Air moves into the lungs during inspiration

A) Because the pressure in the lungs is less than the pressure in the am bient air
B) Because humidification of the air in the lung dilutes the air molecules
C) Because oxygen depletion of alveolar air has lowered the pressure in the lungs
D) Because air molecules diffuse down their concentration gradients
E) Due to contraction of smooth muscle in the trachea