If a lung having a norma

The determination of alveolar ventilation to perfusion ratioinvolves two assumptions. One, that ventilation occurs equally inall alveoli. And second, that blood flow through all capillaries isuniform.Now, if ventilation perfusion ratio drops below 1, then, the amountof perfusion occuring is greater than amount of ventilation. Thisimplies, alveolar air concentration of different gases willgradually start to move towards to the concentration of gases inblood. Therefore, the partial pressure of carbon dioxide willincrease in alveolar air and that of oxygen will decrease.However, the concentration gradient that was present betweenarterial blood and alveolar air now slowly starts to diminish. As aresult, the diffusion of gases slows down. This results inaccumulation of these gases in blood. The partial pressure ofoxygen in blood decreases and the partial pressure of carbondioxide increases.So, option A is correct.