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: Medicine
The key factor in the transport of carbon dioxide as bicarbonate is - 
Select and explain. 
A. The high solubility of CO2  in H2O, B. The presence of Hb in blood, C. The presence of carbonic anhydrase in the erythrocytes, D. The acid nature of carbon dioxide and the alkaline nature of bicarbonate
C: The presence of carbonic anhydrase in the erythrocytes
Answer: C: The presence of carbonic anhydrase in the erythrocytes 
Explanation: None