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
Reducing the size of X-ray beam is achieved by 
Select and explain. 
A. Filtration, B. Photo electric effect, C. Collimation, D. Bezold-brucke effect
C: Collimation
Answer: C: Collimation 
Explanation: None