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': 'Radioactive cobalt emits: \nSelect and explain. \nA. Gamma rays, B. Beta rays, C. Alpha rays, D. Neutrons', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Gamma rays', 'role': 'assistant'}]