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
Pre-renal azotemia is associated with one of the Mowing characteristic feature - 
Select and explain. 
A. UrinaryNa+< lOmmol/L, B. Renal failure index > 1, C. Osmolality < 500, D. Urinary creatinine/P.creatinine ratio < 20
A: UrinaryNa+< lOmmol/L
Answer: A: UrinaryNa+< lOmmol/L 
Explanation: Ref:Harrison 20th edition pg no 291. Values pre renal Azotemia oliguric phase of renal failure BUN/p cr >20:1 10-15:1 Urine sodium meq/L <20 >40 Urine osmolality mosmol/L H20 >500 <350 Fractional excretion of Na <1% >2% Urine analysis (casts) hyaline or granular muddy brown Urine/plasma creatininr >40 <20