GMAT Sentence Correction (SC) | Re: Contrary to earlier conjectures, it may be that increased

Fossil fuels (coal, crude oil and natural gas) are those that have been fossilized from millions of years ago. The process of using them is called combustion, which is to ignite them in a closed chamber such as a furnace, an engine etc; Combustion’s main purpose is to harness heat.

On the contrary burning refers to using sources such as wood that are not fossilized but used immediately. Burning is mostly done in open fires. The purpose here would be mostly for lighting and sometimes to generate