This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: X-RAYS, Subject name: Radiology
Which has the highest penetration power? 
Select and explain. 
A. Neutrons, B. Beta rays, C. Gamma rays, D. X-rays
A: Neutrons
Answer: A: Neutrons 
Explanation: Neutrons have the highest penetration power. The penetration power in increasing order isAlpha< Beta<Xray<Gamma< Neutron