27. Which of the following statements is false in reference to the mammalian synthesis of urea? (A) The carbon atom of urea is derived from mitochondrial . (B) Aspartate directly donates a nitrogen atom for the formation of urea during the urea cycle. (C) The activity of urea cycle is regulated by the rates of synthesis of the four urea cycle enzymes and carbamoyl phosphate synthetase I. (D) Arginine is an inhibitor of the urea cycle. (E) The process of urea production is an energy-consuming series of reactions.