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': 'Ramjford index is used on: \nSelect and explain. \nA. All permanent teeth, B. Selected six permanent teeth, C. Selected twelve permanent teeth, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]