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
The high sodium content of the filtrate in renal medulla is because: 
Select and explain. 
A. 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
A: At the loop of Henle, there is counter current mechanism
Answer: A: At the loop of Henle, there is counter current mechanism 
Explanation: A i.e. At the loop of Henle there is counter current mechanism