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: Forensic Medicine
[{'content': 'Soot in trachea is a sign of? \nSelect and explain. \nA. Postmortem burns, B. Cyanide poisoning, C. Antemortem burns, D. CO poisoning', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Soot in external respiratory passages could be due to antemortem or postmortem burn. But if soot is seen deep in trachea, it is a sign of antemortem burn.', 'role': 'assistant'}]