Why Does Arterial Blood Have a Lower Hydrogen Ion Concentration

Why does arterial blood have a lower hydrogen ion concentration than venous blood?

A) More carbon dioxide remains in the arterial blood leaving the lung capillaries, causing an increase in the amount of carbonic acid and the number of hydrogen ions.
B) Because there are more red blood cells in arteries than veins, the arterial blood has a greater ability to carry fewer hydrogen ions.
C) Less carbon dioxide remains in the arterial blood leaving the lung capillaries, causing a reduction in the amount of carbonic acid and the number of hydrogen ions.
D) The carbon dioxide diffuses out of the venous blood as it moves through the lung capillaries. Therefore, more carbon dioxide remains in the arterial blood leaving the lung capillaries, causing a decrease in the number of hydrogen ions.