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
Which of the following are radioactive? 
Select and explain. 
A. CO 59, B. CO 60, C. Yt 90, D. None
B: CO 60
Answer: B: CO 60 
Explanation: Ans. CO 60