You are presented with the quiz "being preserved under many layers changes vegetation into peat through extreme what?" 

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 "fossils are typically preserved when they are buried under many layers of sand and mud". 

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


 

      heat and pressure     