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 is not a component of counter current multiplier mechanism? 
Select and explain. 
A. Vasa-recta, B. Thick ascending limb of loop of Henle, C. Thin descending limb of loop of Henle, D. Collecting duct
A: Vasa-recta
Answer: A: Vasa-recta 
Explanation: Ans. a. Vasa-recta