Protein molecules are first broken down into amino acids. Amino acids are then converted to pyruvic acid which is then oxidized. One molecule of pyruvic acid after entering into mitochondria undergoes three carboxylation and five oxidation reactions. On oxidation, one molecule of pyruvic acid through Krebs cycle yield 15 molecules of ATP.
Hence, oxidation of one amino acid produces 15 ATP molecules, so oxidation of a dipeptide protein i.e. two amino acids, will produce 2 × 15 = 30 ATP molecules.
So, the correct answer is A.