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: Medicine
[{'content': 'Which differentiating prerenal azotemia with ATN features favouring pre-renal \nSelect and explain. \nA. Urine osmolality > 500 mosmol/kg, B. Sodium spot excretion < 10 ml/L, C. Plasma transferrin/Ig ratio, D. none', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The normal 24-hour urine osmolality is, on average, 500-800 mOsmol/kg of water.\nAfter 12-14 hours of fluid intake restriction, the urine osmolality should exceed 850 mOsmol/kg of water', 'role': 'assistant'}]