Fossil fuels form natural­ly from decaying plants and animals living in ancient seas millions of years ago. this is harvested as crude oil and it contains many hydrocarbons, or molecules that contain hydrogen and carbon in various lengths and structures. the refining process uses separation and a technique called conversion, to turn longer chain molecules such as in diesel fuel are broken into shorter ones forming gasoline. a) chemical processing b) material preparation c) synthetic preservation d) physical transformation