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
[{'content': 'Carbon monoxide poisoning causes \nSelect and explain. \nA. Hypoxic hypoxia, B. Oxygen dissociation curve shifts to left, C. Cyanosis, D. Diffusion capacity of lungs decreases', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]