Read and choose the correct word to fill in the blank

There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs – (34) ________, we call them fossil fuels.

Fossil fuels (35) ________ millions of years to make. But they are not unlimited. We are using up the fuels that were made more than 300 million years ago. They are not (36) ________ like solar power, wind power, hydro power or biomass. Once they are gone they are gone. So, it’s best not to waste fossil fuels.

We can save fossil fuels (37) ________ conserving energy. One simple way to do this is to turn off appliances, TVs and radios that we are not using. We can also turn off lights when no one is in the room. Another way is to go by bike or walk instead of (38) ________ cars or motorbikes.