Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).  

Assertion (A): Compared to cortical nephrons, juxtamedullary nephrons are more suitable for the operation of countercurrent mechanism and play a crucial role in the production of concentrated urine. 

Reason (R): Juxtamedullary nephrons have long loops of Henle with well-developed vasa recta.

In light of the above statements, choose the most appropriate answer from the options given below.

The Henle’s loops of juxtamedullary nephrons are very long and hence are anatomically ideal for the operation of countercurrent mechanism. They have long loops of Henle which extend deep into the medulla. This allows for a prolonged exchange of solutes and water with the medullary interstitium, contributing to the countercurrent mechanism necessary for producing and maintaining a concentration gradient of increasing osmolarity from the outer medulla to the inner medulla. Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine).