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: Physiology
[{'content': 'Which of the following helps to create high medullary osmotic gradient? \nSelect and explain. \nA. Thick ascending loop of henle, B. Vasa recta, C. Counter current exchanger system, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It creats high medullary osmotic gradient.\nIt is by thick ascending loop of henle, collecting duct\n\nMedullary collecting duct.\n\nIt maintains medullary osmotic gradient created by counter current multiplier.\nIt is by Vasa recta', 'role': 'assistant'}]