Natural resources are things that we use that come from Earth. Our natural resources are limited(有限的). This means that they will not _______ forever. Some are renewable, like when you plant a new tree when you _______ one down. Others are not renewable, like when you dig coal(煤) out of the _______. Once it is used, it is gone.People realize the _______ that Earth's natural resources are limited, and can do things to help conserve(节约) those resources. _______ you try to conserve a natural resource, you try to use less of it, so it does not get used up so _______. One way that people