Explanation
The conversion of fumarate to malate in the citric acid cycle is an enzymatic reaction catalyzed by the enzyme fumarase. This reaction does not require the addition of carbon dioxide, water, FAD, or coenzyme A.
Fumarase catalyzes the reversible addition of water across the double bond of fumarate, producing malate. The reaction is as follows:
Fumarate + H2O ↔ Malate
Therefore, the correct answer is B: Water.
