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': 'X-rays are produced by: \nSelect and explain. \nA. Electrons, B. Neutrons, C. Positrons, D. Protons', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Electrons', 'role': 'assistant'}]