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': 'Precarving burnishing is helpful except \nSelect and explain. \nA. Premalgam removal, B. To remove more marginal mercury, C. To remove old amalgam restoration, D. For condensation of marginal mercury', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]