(D) Juxtamedullary nephrons in the mammalian kidney allow the organism to produce hyperosmotic urine.
This statement is true. Juxtamedullary nephrons are a type of nephron found in the mammalian kidney. They have long loops of Henle that extend deep into the medulla, which helps to create a concentration gradient in the medullary interstitium. This gradient enables the production of hyperosmotic urine, which is more concentrated than the body fluids. This adaptation is particularly important for mammals living in arid environments, as it helps them conserve water by excreting more concentrated waste.