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
Speed of X-ray is equal to: 
Select and explain. 
A. Speed of light, B. Speed of electrons in X-ray tube, C. Tube voltage, D. All of the above
A: Speed of light
Answer: A: Speed of light 
Explanation: Ans. Speed of light