The Loops of Henle Are Considered to Function as a Countercurrent

The loops of Henle are considered to function as a countercurrent multiplier because

A) the different segments (the one carrying tubular fluid into the medulla and the one carrying it out) have different permeabilities.
B) the amount of water conserved is related to the force of gravity.
C) as tubular fluid flows in the loop,a concentration gradient is established in the tissue fluids of the medulla.
D) as tubular fluid flows in the loop,it becomes more concentrated in the nephron.
E) active transport in the two segments (the one carrying tubular fluid into the medulla and the one carrying it out) multiplies the concentration gradient in the tubular fluid.