Question

which is true about burning fossil fuels?
most fuels contain a high percentage of carbon
the fuel reacts with nitrogen
clean fuels burn with a yellow flame
little heat energy is released

Explanation:

Fossil fuels like coal, oil, and gas have a high - carbon content. When burning, they react with oxygen, not nitrogen. Clean fuels burn with a blue flame, not yellow. And a large amount of heat energy is released during fossil - fuel combustion.

Answer:

most fuels contain a high percentage of carbon