This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Toxicology, Subject name: Forensic Medicine
[{'content': 'Burtonian line is seen in poisoning by - \nSelect and explain. \nA. Lead, B. Mercury, C. Copper, D. Morphine', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a > b & c' i.e., Lead > Mercury & Copper * Burtonian line is blue line, which is seen on upper gums in lead poisoning.* Similar blue line (but not called burtonian line in these cases) is also seen in poisoning with Mercury (Hg), Copper (Cu), Silver (Ag), bismuth (Bi), and Iron (Fe).", 'role': 'assistant'}]