In this process, the soft tissue of organisms, usually plants, fish, or insects, are preserved when the organism is buried in sediment. then the hydrogen, oxygen, and nitrogen within the organism's body turn to gases and escape. the remaining element leaves a black film in the rock. this type of fossil is called a

The correct answer is carbon film.  

A carbon film or the carbonaceous film refers to a species outline of a fossil. It is a kind of fossil found in any rock when an organic substance is compressed, leaving behind the carbon film or residue.  

When a species is buried beneath the various layers of sediment, the heat and pressure pile up. These circumstances make the liquids and gases to expel from the body, leaving behind a thin film of carbon residue, producing an outline of the original species known as a carbon film.  

carbon atoms, hydrogen, oxygen, and nitrogen.

looks like the answer is     c     to me!