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': 'NMR principle is based on \nSelect and explain. \nA. Positron, B. Neutron, C. Proton, D. Electron', 'role': 'user'}, {'content': 'Answer: C \nExplanation: NMR/MRI principle is based on ability of protons in the body to absorb and emit radio waves when the body is placed in strong magnetic field', 'role': 'assistant'}]