(2) All kinds of nutrients can only be used by the human body after being digested and absorbed, and it is the digestive system that digests and absorbs nutrients. The various systems of the human body are coordinated with each other, so in order to ensure the normal function of the digestive system, we should chew slowly when eating, instead of laughing, eating while playing or wolfing down.

(3) Food contains six kinds of nutrients: protein, sugar, fat, vitamins, water and inorganic salts, each of which is necessary for human body. Among these nutrients, sugar is the most important energy-supplying substance for human body, and the energy consumed by all human activities, including learning, walking, digestion and breathing, mainly comes from sugar; Fat is a spare energy substance in the human body, so the food that people eat the most every day is the food containing more grains. Fat is mainly stored under the skin as a spare energy substance in the human body, and excessive intake can cause obesity and atherosclerosis. It is necessary to reduce consumption as much as possible, and it should not exceed 25 grams per day. protein is an indispensable substance in human tissues, and it is also the main component of various enzymes, antibodies and certain hormones. Children and adolescents are the key period of physical growth and development, so more protein should be supplied to ensure it.

(4) protein is an indispensable substance in human tissues, and it is also the main component of various enzymes, antibodies and some hormones. Children and adolescents are in the critical period of physical growth and development, so they should supply more protein to ensure their growth and development, so they should eat more food in the third and fourth floors of the pyramid.

(5) Coronary heart disease is caused by coronary atherosclerosis, so we should reduce the intake of oils and eat more vegetables and fruits, that is, eat less food on the fifth floor and more food on the second floor.

Therefore, the answer is: (1) b;

（2）B；

(3) cereals; Fat;

(4) protein; Three, four;

(5) 5; Two.