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: Social & Preventive Medicine
[{'content': 'The source of endogenous radiation is \nSelect and explain. \nA. Radon, B. Potassium, C. Thorium, D. Uranium', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e.. Potassium o Radiation is pa of man's environment.", 'role': 'assistant'}]