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
Half life of Rn-222 is: 
Select and explain. 
A. 3 days, B. 3-6 days, C. 4 days, D. 5 days
B: 3-6 days
Answer: B: 3-6 days 
Explanation: Ans. 3-6 days