Digestive enzymes are responsible for

Digestive enzymes are special proteins that speed up chemical digestion. Their job is to break large food molecules into smaller, simpler ones the body can use. For example, amylase breaks starch into maltose and then glucose, protease (like pepsin) breaks proteins into amino acids, and lipase breaks fats into fatty acids and glycerol.

The other options describe jobs done by other parts of the system. Absorption of nutrients into the blood is done mainly by the villi in the small intestine, not by enzymes. Moving food along the gut is done by peristalsis, the squeezing action of muscles in the gut wall.

Controlling the pH is done by substances like hydrochloric acid in the stomach and bile and pancreatic juice in the small intestine. Enzymes only work best at certain pH values; they do not set the pH. So breaking food down into smaller molecules is the correct answer.