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
______________ is not a property of X-rays 
Select and explain. 
A. Ionization, B. Action on photographic film, C. Excitation, D. Collimation
D: Collimation
Answer: D: Collimation 
Explanation: None