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
Which of the following helps to create high medullary osmotic gradient? 
Select and explain. 
A. Thick ascending loop of henle, B. Vasa recta, C. Counter current exchanger system, D. All of the above
A: Thick ascending loop of henle
Answer: A: Thick ascending loop of henle 
Explanation: It creats high medullary osmotic gradient.
It is by thick ascending loop of henle, collecting duct

Medullary collecting duct.

It maintains medullary osmotic gradient created by counter current multiplier.
It is by Vasa recta