This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
[{'content': 'Counter current mechanism, all are true except \nSelect and explain. \nA. Occurs due to opp flow in vasa recta and loop of henle, B. Seen in medullary nephron, C. Helps in creating osmolarity gradient, D. Urea has no role', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Countercurrent mechanism, a system in the renal medulla that facilitates concentration of the urine as it passes through the renal tubules, were medullary osmolarity created by urea.Ref: Ganong&;s review of medical physiology; 24th edition; page no; 687', 'role': 'assistant'}]