The correct option is C Water
The loop of Henle has a descending limb and an ascending limb. As filtrate moves down the loop of Henle, water is reabsorbed, but ions (Na,Cl) aren't. The removal of water concentrates the Na and Cl in the lumen. Now, as the filtrate moves up the ascending limb, Na and Cl are reabsorbed, but water isn't. These two transport properties sets up a concentration difference in NaCl along the length of the loop.