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 presented with ARF with complete anuria but a normal ultrasound. Next investigation is – 
Select and explain. 
A. IVP, B. Antegrade pyelography, C. Retrograde pyelography, D. Radiorenogram
D: Radiorenogram
Answer: D: Radiorenogram 
Explanation: Renal imaging is useful in case of ARF secondary to obstruction. The commonly used imaging modalities in this setting are USG (most common) and nuclear scan (radiorenogram).