I think A is the answer its hard to explain but i hope this helped.
Answer:
Anaerobic respiration resulting in oxygen debt, due to lactic acid accumulation.
Explanation:
After strenuous muscle activity extra oxygen is needed to re-convert lactic acid into glucose and ATP. As you exercise the liver anaerobically converts glucose to lactic acid and carbon dioxide this results in oxygen debts that needs to be repaid later.
Oxygen debt by definition is the amount of oxygen needed by muscles to oxidise lactic acid to glucose after muscle activity.
I believe you're looking for "chemical digestion".
Chemical digestions is where food that we ate is digested into simpler and soluble molecules that can be absorbed by our body. Enzymes are used as a catalyst to speed up the reaction.
One example is the digestion of lipids. Enzyme named lipase is used to speed up the digestion of lipids into 3 fatty acid molecules and 1 glycerol. This way, our body can absorb these simple molecules, and use them in order to make our body function.
On the other hand, physical digestion does not include enzymes, such as chewing in our mouth, therefore, don't mix them up!
