The order of nutrients entering the digestive tract is: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus, in which the digestive organs are mouth, stomach and small intestine. Starch begins to digest in the mouth, protein begins to digest in the stomach, and fat can only be digested in the small intestine.

(1) As can be seen from the figure, the substance B is digested first, then the substance C, and finally the substance A.. It can be judged that A stands for protein digestion, curve B is fat digestion, and curve C is lake digestion. (2) As can be seen from the curve in the figure, starch digestion begins in the mouth, protein digestion begins in the stomach C, and fat digestion begins in the small intestine D; These nutrients are thoroughly decomposed into small molecules in the small intestine, which are soluble in water and can be absorbed by the human body: starch → glucose, protein → amino acids, fat → glycerol and fatty acids.

So the answer is: (1) protein; Fat; Starch. (2) C stomach; D small intestine; Amino acids; glucose