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
Quality of the X-ray beam is governed by: 
Select and explain. 
A. kVp, B. mA, C. Filament current, D. Length of the X-ray tube
A: kVp
Answer: A: kVp 
Explanation: None