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': 'Nowadays radium is not used in the Rx of cancer because: \nSelect and explain. \nA. It decays faster and needs frequent replacement, B. It decays into daughter Radon which is a constant hazard, C. It has a very long half life, D. It is a very unstable element', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. It decays into daughter Radon which is a constant hazard', 'role': 'assistant'}]