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 bogs are characterized by cushion-like vegetation and an accumulation of peat. Given these facts, what has its soil and mud changed by extreme heat over long periods of time among the following options:
- elms
 - bogs
 - bamboo
 - earth
 - deltas
 - coal
 - corn
 - swea


 

  bogs       