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': 'Which of the following are radioactive? \nSelect and explain. \nA. CO 59, B. CO 60, C. Yt 90, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. CO 60', 'role': 'assistant'}]