This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urology, Subject name: Surgery
What is this study? 
Select and explain. 
A. Retrograde Pyelogram, B. Ultrasound, C. X Ray KUB, D. Contrast CT KUB
A: Retrograde Pyelogram
Answer: A: Retrograde Pyelogram 
Explanation: Retrograde ureterogram demonstrating the collecting system. The radiolucent filling defect in the renal pelvis is caused by radiolucent calculus