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
Radioisotopes which is used in teletherapy: September 2011 
Select and explain. 
A. Ra-226, B. Cs-137, C. Co-60, D. 1r-192
C: Co-60
Answer: C: Co-60 
Explanation: Ans. Co-60