Fact 1: Heat and pressure change the remains of prehistoric living things into natural gas.

Fact 2: Natural gas is the cleanest of the fossil fuels.

Given the two facts above, answer the question "Where do fossil fuels come from?" with the following options: 
- Dead prehistoric beings
 - Under water
 - basic building blocks of life
 - dead organisms
 - decaying trees
 - burning coal
 - A factory
 - Outerspace


 

 Dead prehistoric beings        