Answer:
a. oxidize NADH to NAD+
Explanation:
Alcohol fermentation and lactic acid fermentation share a common step that is glycolysis. Since the organisms or cells that carry out the fermentation lack oxygen, oxidative phosphorylation can not oxidize NADH into NAD+. Without the supply of NAD+, glycolysis cannot occur as NAD+ serves as electron acceptor during redox reactions of glycolysis.
To maintain the continuity of glycolysis, alcohol fermentation and lactic acid fermentation oxidize the NADH into NAD+ which in turn enter the glycolysis.
