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
[{'content': 'A dense persistent nephrogram may be seen in all of the following except – \nSelect and explain. \nA. Acute ureteral obstruction, B. Systemic hypertension, C. Severe hydronephrosis, D. Dehydration', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hypotension causes persistent dense nephrogram (not hypertension).', 'role': 'assistant'}]