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
Investigation in a patient of oliguria revealed Urine osmolity 620 mosm/kg Urine sodium :12mmol/L Urine /plasma urea ratio :13 :1 The most likely diagnosis is - 
Select and explain. 
A. Prerenal acute renal failure, B. Acute tubular recrosis, C. Acute cortical necrosis, D. Urinary tract obstruction
A: Prerenal acute renal failure
Answer: A: Prerenal acute renal failure 
Explanation: None