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
For teletherapy, isotopes commonly used are 
Select and explain. 
A. 1-123, B. Cs-137, C. Co-60, D. Tc-99
C: Co-60
Answer: C: Co-60 
Explanation: C i.e. Co-60