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': 'What is the modern approach treatment of a discoloured crown? \nSelect and explain. \nA. Composite restoration, B. Full crown, C. Bleaching, D. Implant', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]