Which of the choices below gives a true example of how a natural resource can be renewed?
When an area's natural gas has been used up, oxygen can replace the gas.
When forests have been cut down, new native trees can be planted.
When all of the coal is gone from a mine, new coal can be grown in its place. When the wind is calm, electric fan can be turned on to make the windmills move.
When the wind is calm, electric fans can be turned on to make the windmills move.
