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': 'Simple and effective index of monitoring periodontal status of individual by general practitioner is \nSelect and explain. \nA. PSR, B. PI, C. CPITN, D. PDI', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]