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
'Rim' and 'ball' nephrograms in intravenous urography are seen in – 
Select and explain. 
A. Normal kidneys, B. Acute obstructive nephropathy, C. Chronic obstructive nephropathy, D. Chronic renal failure
C: Chronic obstructive nephropathy
Answer: C: Chronic obstructive nephropathy 
Explanation: None