Answer: Option (c) is the correct answer.
Explanation:
Coal is a black-brownish sedimentary rock. It is produced from giant ferns, reeds and mosses which are present in the Earth.
For about millions of years when all these plants grew then due to the changes caused by heat and pressure there will occur changes in the plant layers.
These layers were fall short of oxygen and results in formation of carbon rich deposits.
Hence, coal takes millions of years to form.
