如图所示，下列说法正确的是（　　）

下列式子：x²+2，$\frac{1}{a}$+4，$\frac{3a{b}^2}{7}$，$\frac{ab}{c}$，﹣5x，0中，整式的个数是（　　）

    Natural resources are things that we use that come from Earth.  Out natural resources are limited(有限的). This means that they will not1 forever.

    Some are renewable, like when you plant a new tree when you2one down. Others are not renewable, like when you dig coal out of the 3.Once it is used, it is gone. People realize the4that Earth's natural resources are limited, and can do things to help save those resources.5you try to save a natural resource, you try to use less of it, so it does not run out so 6 One way that people save fuel, like gasoline, is by riding a bicycle or walking when the 7is short instead of driving everywhere. Water is a very important natural resource because we all need it to stay8. We can keep water9making sure that our pipes and taps do not leak(漏). We can also make 10 choices to save water, like only using the dishwasher or washing machine when they are full.

    Everyone can make contributions to protecting natural resources.