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': 'The high sodium content of the filtrate in renal medulla is because: \nSelect and explain. \nA. At the loop of Henle, there is counter current mechanism, B. Increased blood flow to vasarecta, C. Increased excretion of Na* from PCT, D. Increased absorption of Na from PCT', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. At the loop of Henle there is counter current mechanism', 'role': 'assistant'}]