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
Definition and Detail Describes: 
Select and explain. 
A. Image sharpness., B. Increases as focal spot size reduce, C. Reduces as focal spot size increases., D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None