题目

Good health is the most valuable thing a person can have, but one cannot take good health for granted. It is important to remember that the body needs proper care in order to be healthy. There are three things that a person can do to help stay in good shape: eat right food, get enough sleep, and exercise regularly.Proper nutrition is important for good health. Your body cannot work well unless it receives the proper kind of “fuel”. Don't eat too much food with lots of sugar and fat. Eat plenty of foods high in protein (蛋白质) , like meat, fish, eggs and nuts. Vegetables and fruits are 8．已知矩形ABCD的周长为20cm．若设AB=xcm，BC=ycm．请写出y与x的函数关系式并写出自变量x的取值范围．