This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiotherapy, Subject name: Radiology
Maximum penetrating radiation among the below is 
Select and explain. 
A. Electrons, B. Gamma rays, C. Alpha paicles, D. Beta paicles
B: Gamma rays
Answer: B: Gamma rays 
Explanation: The penetrating power of alpha rays, beta rays, and gamma rays varies greatly. Alpha paicles can be blocked by a few pieces of paper. Beta paicles pass through paper but are stopped by aluminium foil. Gamma rays are the most difficult to stop and require concrete, lead, or other heavy shielding to block them.Reference: Eric J Hall Textbook of Radiobiology for Radiologist; 5th edition