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 Cobalt-60 
Select and explain. 
A. 30 years, B. 5.2 years, C. 74.5 days, D. 6 hours
B: 5.2 years
Answer: B: 5.2 years 
Explanation: Cobalt-60 – 5.2 years
Cesium-137 – 30 years
Iridum-192 – 74.5days