Answer
A.
Work Step by Step
A. describes the normal function of NAD+: to receive electrons and carry them and the energy associated with them. B. can be eliminated because NAD+ helps enzymes but is not an enzyme itself, and C. is wrong since anaerobic respiration uses carbon dioxide or sulfate as the final acceptor, not NAD+. D. is wrong since ATP is used to make NAD+, not the other way round.