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': 'Purple lining over gums is seen in which chronic poisoning: \nSelect and explain. \nA. Magnesium, B. Lead, C. Copper, D. Mercury', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Copper', 'role': 'assistant'}]