The Final Step of the Citric Acid Cycle Oxidizes Malate

The final step of the citric acid cycle oxidizes malate to oxaloacetate and reduces NAD⁺. What is the purpose of this step?

A) to replenish the supplies of NAD⁺
B) to replenish free CoA
C) to regenerate oxaloacetate to attach another acetate molecule
D) to produce ATP by substrate-level phosphorylation
E) to produce ATP by oxidative phosphorylation