seas that have evaporated. natural gas subjected to heat. melted and cooled metamorphic rock. plant remains decomposed under pressure.
I gave my students this multiple choice question: Coal is formed from

Only one answer is correct among these 4 choices:
- seas that have evaporated.
- natural gas subjected to heat.
- melted and cooled metamorphic rock.
- plant remains decomposed under pressure.

Could you tell me which one is correct?

plant remains decomposed under pressure.