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': 'PMA index given by Schour and Massler is a method of assessing \nSelect and explain. \nA. Periodontitis, B. Oral hygiene, C. Amount of calculus, D. Gingivitis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]