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': 'In medical radiotherapy linear particle accelerator emits \nSelect and explain. \nA. Electron and photons, B. Electron and positrons, C. Neutrons and positrons, D. Neutrons only', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]