(1) The small intestine is large, and it is the longest in the digestive tract, about 5-6 meters long; There are many annular folds on the inner surface of the small intestine wall, and there are many villous protrusions on the folds, which are called small intestine villi. Because of the existence of annular folds and small intestine villi, the absorption area of small intestine is greatly increased, reaching more than 211 square meters. The wall of villi of small intestine is very thin, which is composed of only one layer of epithelial cells, and there are abundant capillaries and lymphatic capillaries in villi, which is beneficial to the absorption of nutrients by small intestine. Intestinal glands secrete intestinal juice; The small intestine contains pancreatic juice, bile and other digestive juices, which can digest starch, fat and protein. Therefore, the small intestine is the main place for digestion and absorption.

D mainly contains starch, and H contains more vitamins, so except DH, the foods of chicken, fish, lean meat, eggs and shrimp are rich in protein.

(2) The body of arthropods is composed of many segments. Feet and antennae are also segmented. The main groups of arthropods are Insecta, Polypoda, Arachnida and Crustacea, so the shrimps and crabs in the picture belong to arthropods. In the animal kingdom, birds and mammals are covered with fur or feathers, which have a good heat-generating and heat-dissipating structure, and their body temperature does not change to warm-blooded animals with the change of external temperature. Therefore, a, g and b are from warm-blooded animals in the picture. Besides paying attention to food safety, we should also pay attention to reasonable diet. Only in this way can we benefit the healthy growth of human body, otherwise unreasonable eating habits such as partial eclipse will lead to malnutrition or overnutrition. < P > So the answer is: (1) Small intestine? D、H（2）C、F? A, G and B(3) Reasonable nutrition and balanced diet.