You are presented with the quiz "What does vegetation change into after being buried under soil?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "being burried under soil and mud changes vegetation into peat through extreme heat and pressure in a swamp over a long period of time" and "peat moss from bogs is also useful in gardens and as an alternative fuel source". 

So, what's the best answer to the question?


 

        fuel   