Carbon dioxide enters the blood at the capillaries. here, some of the carbon dioxide binds to the region of hemoglobin.

Carbon dioxide enters the blood at the systemic capillaries. Here, some of the carbon dioxide binds to the globin region of hemoglobin. The systemic capillaries function to carry oxygenated blood for the tissues of the body. As it enters these capillaries, blood would lose oxygen and in return gain CO2 molecules due to the difference in pressure of the tissues and the blood.

The answer to this is b