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
CO has higher affinity for hemoglobin. The affinity of CO for Hb as compared to O2 is approximately: 
Select and explain. 
A. 120 times, B. 210 times, C. 240 times, D. 360 times
B: 210 times
Answer: B: 210 times 
Explanation: CO binds to hemoglobin with an affinity more than 200 times that of oxygen, and this not only directly reduces the oxygen-carrying capacity of blood, but fuher promotes tissue hypoxia by shifting the oxyhemoglobin dissociation curve to the left. CO may also cause harm by other mechanisms including direct disruption of cellular oxidative processes, binding to myoglobin and hepatic cytochromes, and peroxidation of brain lipids. Ref: Bennett M.H., Mitchell S.J. (2012). Chapter e52. Hyperbaric and Diving Medicine. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.