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': 'The primary driving force for counter current Multiplier system is:(2018) \nSelect and explain. \nA. Medullary hyperosmolarity, B. Reabsorption of Na+ in thick ascending limb, C. Action of ADH aquaporin channels, D. Urea recycling', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Concentrating mechanism depends on the maintenance of a gradient of increasing osmolality along the medullary pyramids. This gradient is produced by the operation of the loops of Henle as countercurrent multipliers and maintained by the operation of the vasa recta as countercurrent exchangers. Ref:- Ganong, pg num:- 685', 'role': 'assistant'}]