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
The source of endogenous radiation is – 
Select and explain. 
A. Radon, B. Potassium, C. Thorium, D. Uranium
B: Potassium
Answer: B: Potassium 
Explanation: None