This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, 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: Park's textbook of preventive and social medicine 23rd edition. * Man is also subjected to internal radiation,i.e, from radioactive matter stored in the body tissues, it includes minute quantities of uranium , thorium, isotopes of potassium,strontium and carbon.", 'role': 'assistant'}]