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': 'Principles of Linear accelerators is used in \nSelect and explain. \nA. X-rays, B. Gamma - rays, C. Alpha rays, D. Infrared rays', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]