Acetyl CoA is carboxylated to malonyl CoA during fatty acid biosynthesis: a) for thermodynamic purposes. Removal of the carboxyl (CO2) group during fatty acid biosynthesis releases energy which makes the process feasible from a thermodynamic standpoint. b) in order to transport the acetyl CoA molecules into the mitochondrial matrix, the site of fatty acid biosynthesis. c) to produce an even carbon precursor for the production of fatty acids. d) to prevent the formation of ketone bodies.