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': 'Black gun powder made of: \nSelect and explain. \nA. Potasium nitrate, B. Charcoal, C. Sulfur powder, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: A i.e. Potassium nitrate; B i.e. Charcoal; C i.e. Sulfur', 'role': 'assistant'}]