Final answer:
C) external respiration
External respiration refers to the gas exchange between the alveoli and pulmonary blood, driven by partial pressure differences of oxygen and carbon dioxide.
Step-by-step explanation:
The gas exchange between the pulmonary blood and alveoli is called external respiration. This process occurs in the alveoli of the lungs, where there are thin-walled pulmonary capillaries surrounding the alveoli. Due to the partial pressure differences, oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses in the opposite direction, from the blood into the alveoli.