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 only valid method to assess periodontal regeneration is \nSelect and explain. \nA. Radiographic analysis, B. Clinical attachment level, C. Reentry operation, D. Histologic analysis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Clear evidence of a new attachment apparatus can be determined only by histologic analysis of tissue blocks obtained from the healed area.', 'role': 'assistant'}]