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 index used to record the plaque score is \nSelect and explain. \nA. PMA Index, B. Silness and Loe Index, C. Green and vermillion Index, D. Russell's index", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]