Which statement is true?
a. oxygen uptake decreases as the body requires more oxygen and faster removal of carbon dioxide.
b. the exchange of oxygen and carbon dioxide occurs in the bronchioles in the lungs.
c. oxygen diffuses into the bloodstream because there is a higher concentration of oxygen in the lungs than in the blood flowing into them.
d. the blood that flows into the lungs and past the alveoli is blood that has just circulated around the body and is rich in oxygen.