Enzymes and pH question

answer is D
can someone simply explain thanks


enzymes in the stomach have an optimum pH around 1,5 and break down proteins into smaller peptides, so enzyme A must have protein as substrate

enzymes in the small intestine have an optimum between 6-8 and break down lipids, carbohydrates and peptides into amino acids, so the possible substrates are lipids or proteins. amino acids would be the product not the substrate

Answer must be D)