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
Most common used rays for radiotherapy – a) X raysb) γ rays c) α raysd) β rays 
Select and explain. 
A. ab, B. bc, C. ac, D. cd
A: ab
Answer: A: ab 
Explanation: "Several different types of radiation are used to treat patients with malignant conditions. The most frequently used  forms of radiation for cancer therapy, however are , high energy X-rays and gamma rays".