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
During the production of X-rays, how much of electron energy is converted into heat 
Select and explain. 
A. 99%, B. 94%, C. 89%, D. 84%
A: 99%
Answer: A: 99% 
Explanation: None