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': 'Blue line on the gums is seen in chronic ..... poisoning : \nSelect and explain. \nA. Fig, B. Pb, C. Ag, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: B i.e. Pb > A i.e. Hg, C i.e. Ag', 'role': 'assistant'}]