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
Which of the following techniques uses piezoelectric crystals? 
Select and explain. 
A. Ultrasonography, B. NMR imaging, C. X-ray diffraction, D. Xeroradiography
A: Ultrasonography
Answer: A: Ultrasonography 
Explanation: Ans. Ultrasonography