The correct answer is (c), anthracite. Anthracite is the highest grade of coal, and it is the most expensive. It is also the most energy-rich type of coal, and it burns with a very low ash content. Anthracite is used in power plants and in industrial applications where a high-quality fuel is required.
Lignite is the lowest grade of coal, and it is the least expensive. It is also the least energy-rich type of coal, and it burns with a high ash content. Lignite is used in power plants and in industrial applications where a low-cost fuel is acceptable.
Peat is a type of coal that is not yet fully formed. It is made up of plant material that has been buried and subjected to heat and pressure over time. Peat is used as a fuel in some parts of the world, but it is not as energy-rich as coal.
Bituminous coal is a type of coal that is between lignite and anthracite in quality. It is more energy-rich than lignite, but it is not as energy-rich as anthracite. Bituminous coal is used in power plants and in industrial applications.