In animals, the breakdown of food molecules occurs in three stages: _______________.
选项：

A:Stage 1 mostly occurs outside cells, with the breakdown of large food molecules in the mouth and the gut—although intracellular lysosomes can also digest such large molecules.
B:Stage 2 starts intracellularly with glycolysis in the cytosol, and ends with the conversion of pyruvate to acetyl groups on acetyl CoA in the mitochondrial matrix.
C:Stage 3 begins with the citric acid cycle in the mitochondrial matrix and concludes with oxidative phosphorylation on the mitochondrial inner membrane. The NADH generated in stage 2 adds to the NADH produced by the citric acid cycle to drive the production of large amounts of ATP by oxidative phosphorylation.
D:all the above.