Average Human Lung Capacity Is 6 L,but a Typical Breath

Multiple Choice

Average human lung capacity is 6 L,but a typical breath is only about 400 ml;inhaled air only directly reaches the bronchi.How does the oxygen get from the bronchi to the alveoli?

A) It's transported by the blood in the bronchi and delivered to the alveoli.
B) The next inhalation moves it a little closer-by the ninth or tenth inhalation it has reached the alveoli.
C) It diffuses down the bronchioles because its concentration in the alveoli is low.
D) Oxygen molecules are relatively heavy;they simply flow under the influence of gravity down into the alveoli.