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: Radiology
[{'content': 'Which of the following techniques uses piezoelectric crystals? \nSelect and explain. \nA. Ultrasonography, B. NMR imaging, C. X-ray diffraction, D. Xeroradiography', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Ultrasonography', 'role': 'assistant'}]