(2) Starch is digested into maltose in the oral cavity and glucose in the small intestine, so curve A is the digestion of starch; Protein is digested in the stomach and finally in the small intestine, so curve B is protein's digestion; Fat can only be digested in the small intestine, so curve C is the digestion of fat.
(3) Food contains six nutrients: protein, sugar, fat, vitamins, water and inorganic salts. Protein is the basic substance of human cells, which plays a major role in the growth and development of the body and the repair and renewal of cells. Eggs are rich in protein, protein, digested in the stomach, and finally digested into amino acids in the small intestine, so curve B is digested by protein.
(4) If the human body lacks vitamin C, it is prone to scurvy.
So the answer is: (1) There is too much salt in food; Lack of fresh vegetables and fruits;
(2) A; Maltose; Glucose;
(3) protein; b; Amino acids;
4 vitamin C.