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
[{'content': 'CO poisoning is characterized by -a) Lt. shift of O2 dissociation curveb) ↓ PaCO2c) ↓ P50d) ↓ O2 Contente) Smoking is a predisposing factor \nSelect and explain. \nA. acd, B. bde, C. abd, D. ade', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]