We use alternatives .but without a drop of Nat. resource we can't do anything.
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We can use many alternative recourses instead of the natural resources like solar energy, tidal energy, wind energy and even we can use biological energy sources. now-a-days we can find that the natural resources are being depleted a lot because of burning more and more fossil fuels. for our energy sources we burn fossil fuels but if we don't have fossil fuels we need to do so much research for other alternative and even our future generations won't be having the natural resources. hence we need to use other alternative resources like solar energy, tidal energy and wind energy.  
hope so my answer is useful and mark as best if possible ..!