This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Medicine
[{'content': 'Plasma urea / creatinine ratio of 20:1 may be seen in- \nSelect and explain. \nA. Rhabdomyolysis, B. Ureteric calculi, C. Pre-renal failure, D. Chronic glomerulonephritis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Background. A blood urea nitrogen (BUN)/creatinine ratio (BCR) >20 (0.081 in international unit) is used to distinguish pre-renal azotemia (PRA) and acute tubular necrosis (ATN). However, there is little evidence that BCR can distinguish between these two conditions and/or is clinically useful Ref Harrison20th edition pg 299', 'role': 'assistant'}]