The fossil fuels are [?], oil and natural [?]. Fossil fuels are our main source of . The supply of [?] fuels is finite - this means that they cannot [?] forever and the supply will run out some time in the future.
We need to conserve our supplies so that they will last for as long as possible.
As the stocks of fossil fuels get used up we will need to use alternative, [?], sources of energy such as [?], wind and solar power.
When fuels burn they use up [?] from the air.