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
Which of the following is s/o ATN? 
Select and explain. 
A. FENa <1, B. renal failure index <1, C. blood urea nitrogen/cr ratio <20, D. urine osmolality >1.010
C: blood urea nitrogen/cr ratio <20
Answer: C: blood urea nitrogen/cr ratio <20 
Explanation: Ans c (Blood urea nitrogen/cr ratio<20)Harrison 17 page no: 1756, table 273-2indicespre-renalAINUrine osmolality>500<350Urine sodium<20>40urine/serum creatinine>40<20 >1.2>1.2FENa<1>1Renal failure index<1>1Urine sp gravity>1.020<1 010 :