This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals in Radiology, Subject name: Radiology
[{'content': 'Frequency of sound waves used in USG - \nSelect and explain. \nA. < 1000 Hz, B. > 5000 Hz, C. > 10000 Hz, D. > 20000 Hz', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Frequency of sound waves used in usg is >20000Hz.', 'role': 'assistant'}]