Final answer:
The citric acid cycle produces NADH and FADH2, which transport high-energy electrons that power oxidative phosphorylation to generate ATP.
Step-by-step explanation:
The citric acid cycle, also known as the Krebs cycle, is a series of redox and decarboxylation reactions that remove high-energy electrons and carbon dioxide. These high-energy electrons are stored in molecules of NADH and FADH2. These molecules then transport the high-energy electrons to the electron transport chain in the mitochondria, where ATP is generated through oxidative phosphorylation. Therefore, option d is the correct answer - transporting high-energy electrons that power oxidative phosphorylation.