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: Dental
[{'content': 'Conventional dental amalgam alloy contains: \nSelect and explain. \nA. Silver, tin, copper and zinc, B. Silver, mercury, copper and zinc, C. Silver, tin, palladium and zinc, D. Silver, copper, iridium and mercury', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]