This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Most of the CO2 transported in the blood is 
Select and explain. 
A. Dissolved in plasma., B. In carbamino compounds formed from plasma proteins., C. In carbamino compounds formed from hemoglobin., D. In HCO3–
D: In HCO3–
Answer: D: In HCO3– 
Explanation: The CO2 that diffuses into red blood cells is rapidly hydrated to H2CO3 because of the presence of carbonic anhydrase.
The H2CO3 dissociates to H+ and HCO3-, and the H+ is buffered, primarily by hemoglobin, while the HCO3- enters the plasma.