The correct option is C Blood buffers
The bicarbonate buffering system of blood is an important buffer system in the acid-base homeostasis of living things, including humans. As a buffer, it tends to maintain a relatively constant plasma pH and counteract any force that would alter. In this system, carbon dioxide CO2 combines with water H2O to form carbonic acid H2CO3, which in turn rapidly dissociates to form hydrogen ions H+ and bicarbonate HCO3 as shown in the reactions below.
CO2+H2O⇄H2CO3⇄HCO−3+H+
The carbon dioxide - carbonic acid equilibrium is catalyzed by the enzyme carbonic anhydrase; the carbonic acid - bicarbonate equilibrium is simple proton dissociation/association and needs no catalyst. Any disturbance of the system will be compensated by a shift in the chemical equilibrium.