The correct answer is: a) Lignite.
Lignite is the lowest rank of coal, and is found in the youngest coal seams. It is soft and brown in color, and has a high moisture content. Lignite is not as good for burning as other types of coal, but it is the most abundant type of coal in the world.
Bituminous coal is a higher rank of coal than lignite, and is found in older coal seams. It is black in color, and has a lower moisture content than lignite. Bituminous coal is better for burning than lignite, and is used to generate electricity and produce steel.
Anthracite is the highest rank of coal, and is found in the oldest coal seams. It is black in color, and has a very low moisture content. Anthracite is the best type of coal for burning, and is used to generate electricity and produce steel.
Peat is a type of coal that is not yet fully formed. It is found in bogs and swamps, and is made up of plant material that has been buried and compressed over time. Peat is not a good fuel, but it can be used to make fertilizer and other products.