The correct answer is D. Anthracite.
Anthracite is the highest rank of coal, and it has the lowest proportion of volatile matter. Lignite is the lowest rank of coal, and it has the highest proportion of volatile matter. Bituminous coal is between lignite and anthracite in rank, and it has a higher proportion of volatile matter than anthracite but a lower proportion than lignite. Peat is not a type of coal, but it is a precursor to coal. It has a very high proportion of volatile matter.
Volatile matter is the part of coal that is released as gas when coal is burned. The proportion of volatile matter in coal affects the way that coal burns. Coal with a high proportion of volatile matter burns more quickly and with a higher flame than coal with a low proportion of volatile matter.
Anthracite is the most desirable type of coal because it burns with a low flame and produces a lot of heat. It is also the most expensive type of coal. Lignite is the least desirable type of coal because it burns with a high flame and produces less heat. It is also the cheapest type of coal.