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
The' 1/2 life of 1131 is: 
Select and explain. 
A. 8 hours, B. 2 days, C. 5.2 days, D. 8 days
D: 8 days
Answer: D: 8 days 
Explanation: Ans. 8 days