1)petroleum and natural gas are formed in the 2) refers to the things that exists freely in nature or human use
3) during the period the earth was covered with swampy forest's
4) is the mixture of hydrogen, methane, carbon monoxide, and other gases
5)natural gas mainly consists of
6)are the chemicals derived from petroleum and natural gas
7) the process of refining of petroleum is carried out in refineries and is called
8) is used to generate power and to manufacture other fuels like coke and coal tar