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
A patient presents with ARF with a normal ultrasound repo. The next most useful investigation is: 
Select and explain. 
A. Renal angiography, B. Retrograde pyelography, C. Intravenous pyelography, D. DTPA scan
D: DTPA scan
Answer: D: DTPA scan 
Explanation: Ans. DTPA scan