Given That Only Some Fermentation Pathways Generate ATP for Use

Given that only some fermentation pathways generate ATP for use by an organism, what is the main purpose of fermentation reactions?

A) to produce carbon skeletons for the Krebs cycle
B) to produce lactic acid for the cells to use for energy
C) to recycle NADH to NAD⁺ so that the NAD⁺ pool is not tied up
D) to recycle FADH₂ to FAD⁺ so that the FAD⁺ pool is not tied up
E) to synthesize NADH for use in the electron transport chain