This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 1, Subject name: Physiology
[{'content': 'Oxygen dissociation curve shifts to left in all except: \nSelect and explain. \nA. Alkalosis, B. Hypercapnia, C. Fetal Hb, D. CO poisoning', 'role': 'user'}, {'content': 'Answer: B \nExplanation: When the O2 affinity for Hb is increased, the dissociation curve shifts to the left. O2 has less affinity for Hb which is in "T-state". When Hb is snapped into "R-state", O2 affinity for it increases. Increased affinity of O2 for Hb/shift to the left Decreased H+/alkalosis Decreased PCO2 Decreased temperature Decreased 2,3-DPG HbF CO poisoning Stored blood (2,3-DPG decreases) NO & H2S (bind to Hb; snap it into "R-state")', 'role': 'assistant'}]