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 pattern of vibration of magnetostrictive type of ultrasonic scaler is \nSelect and explain. \nA. Elliptical, B. Linear, C. Back and forth, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]