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
Gamma knife – a) Steel knifeb) Used for cutting tumours in difficult locationc) Cobalt is usedd) Recovery delayed 
Select and explain. 
A. a, B. c, C. ac, D. bc
D: bc
Answer: D: bc 
Explanation: Gamma knife is used for stereotactic radiosurgery for tumors in difficult locations e.g. deep seated brain tumors. It contains Cobalt - 60 sources.