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': 'NMR based in the principle of ? \nSelect and explain. \nA. Electron beam, B. Proton beam, C. Magnetic field, D. Neutron beam', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Proton Beam', 'role': 'assistant'}]