How does fumarate link the urea cycle to the citric acid cycle?

• A. Fumarate is used to synthesize ATP in the citric acid cycle.
• B. Fumarate is converted into argininosuccinate in the citric acid cycle.
• C. Fumarate is directly converted into glucose in the citric acid cycle.
• D. Fumarate produced in the urea cycle enters the citric acid cycle, where it is converted to malate and then oxaloacetate.

Answer: (D)