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
NMR based in the principle of 
Select and explain. 
A. Electron beam, B. Proton beam, C. Magnetic field, D. Neutron beam
D: Neutron beam
Answer: D: Neutron beam 
Explanation: NMR stands for Nuclear Magnetic Resonance. MRI is based on the ability of a small number of protons within the body to absorb and emit radio wave energy when the body is placed in the strong magnetic field.