Coal was formed from the remains of ferns, trees, and grasses that grew in swamps over 300 million years ago. The plants
partially decayed as these layers formed beds of peat. Peat is the earliest stage in the formation of coal. Ancient seas covered the
swamps and slowly deposited layers of sand and mud over them. These sediments and added rock layers exerted great pressure
on the peat for thousands of years. The peat was transformed into lignite or brown coal Millions of years later, increasing
pressure and heat changed the lignite into bituminous or soft coal and finally into anthracite or hard coal.
Depending upon its composition, each type of coal burns differently. The older the coal, the harder the coal, and the greater
percentage of present.

A. carbohydrates

B. carbon

C. oxygen

D. water