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': 'What is seen in CO poisoning? \nSelect and explain. \nA. Oxygen curve shifts to left, B. Hypoxic hypoxia, C. Cyanosis, D. Diffusion capacity of lung decreases', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]