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 doesn't produce radiation hazard: September 2006 \nSelect and explain. \nA. MRI, B. Doppler USG, C. Both of the above, D. None of the above", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C: Both of the above MRI is a noninvasive imaging technique that does not involve exposure to ionizing radiation. USG is based on piezoelectric effect and free from radiation.', 'role': 'assistant'}]