What Is the Function of Urea Reabsorption in the Collecting

What is the function of urea reabsorption in the collecting ducts of the kidney?

A) It restores the correct concentration of blood urea.
B) It increases the osmotic concentration of the interstitial fluid in the renal medulla so that more water can be extracted from the urine.
C) It reduces the salinity of the renal medulla and thus helps regulate how much water is reabsorbed from the urine.
D) It moves the urea into the ascending limb of the loop of Henle so that it can be excreted from there in the urine.