The countercurrent multiplier is a system by which the:. a. nephron loop multiplies the concentration of salts in the interstitial fluid of the kidney medulla.
b. nephron loop dilutes the concentration of solutes in the tubular fluid at its hairpin turn.
c. vasa recta secretes multiple amounts of metabolic wastes against their concentration gradient.
d. vasa recta becomes more concentrated with nitrogenous wastes than the urine.

Option A.

nephron loop multiplies the concentration of salts in the interstitial fluid of the kidney medulla.

Explanation:

countercurrent multiplier is a system that utilize energy that create osmotic gradients and enable reabsorption of water thereby increase concentration of urine. The countercurrent multiplier uses electrolyte pumps there by making the nephron loop increase the concentration of salts in the interstitial fluid of the kidney medulla because it allows the nephron to reabsorb alot of water and and increase the concentration of urine for excretion while at the same time using as little energy as possible.