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': 'Pre-renal azotemia is associated with one of the following characteristic feature : \nSelect and explain. \nA. Urinary Na+ < 10 mmol/L, B. Renal failure index > 1, C. Osmolality < 500, D. Urinary creatinine / P. creatinine ratio < 20', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer is A (Urinary Na+ < 10 mmol/litre): Prerenal azotemia is associated with a urinary sodium excretion of less than 10 mmol/L.', 'role': 'assistant'}]