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': 'Mobility of teeth is measured using: \nSelect and explain. \nA. Periodontometer, B. Periotron, C. Spechtometer, D. Densitometer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]