Why Is the Actual Flow of Air into the Alveoli

Why is the actual flow of air into the alveoli during inspiration passive?

A) because there is a continuous column of air from the pharynx to the alveoli
B) because the lungs are surrounded by the thoracic wall
C) because the alveoli have a very large surface area
D) because the intercostal muscles are involved
E) because the diaphragm is involved