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': 'The most common reason of replacement of dental restoration: \nSelect and explain. \nA. Secondary caries, B. Tooth fracture, C. Restoration fracture, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The most common reason for the replacement of dental restorations is secondary caries at the gingival tooth-restoration margin.', 'role': 'assistant'}]