题目

Just like a car engine needs petrol (汽油), your body needs fuel (燃料;养料). It needs food!The things you eat and drink are turned into energy.You need energy for everything-playing, walking, running, thinking-even sleeping.Feeling hungry may mean you are running low on energy. If it is not meal time, you may need a snack to refuel.But what sort of snack should you eat? This is like choosing the right fuel for a car. Some cars, such as racing cars, need the best fuel to go fast and keep their engines running smoothly.So, if you want to be at your most lively, choose the best fuel. This 9．下列对应关系中，能构成从集合A到集合B的映射的是（　　）A．A={0，2}，B={0，1}，f：x→y=$\frac{x}{2}$B．A={-1，-2，-3，1，2}，B={1，4}，f：x→y=x2，x∈A，y∈BC．A=R，B={y|y＞0}，f：x→y=$\frac{1}{{x}^{2}}$D．A=Z，B=N*，f：x→y=|x|，x∈A，y∈B