The right answer is NAD+ (NADH).
NAD (Nicotinamide-adenine-dinucleotide) is a coenzyme found in cells. It is a dinucleotide, insofar as the molecule consists of a first nucleotide, whose nucleic base is adenine, united to a second nucleotide, the base of which is nicotinamide. NAD exists in an oxidized form, denoted NAD+, and a reduced form, denoted NADH.
