ther are three kinds of food to maitain lfe.first is carbohydrate,which synthesis the nessissary
glucose and enzymes of biological process is widely in annimals and plants,it contains sugar,starch and cellulose .all of them can provide energy for people.the second is fat,which is more condenser food energy than carbohydrate ,butit only can be used as saving energy than using energy.the third is protain,which is composed of macromolecules like hydrogen,oxygen and nitrogen.it is not to provide energy ,but the necessary material to build a life.
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