When the material A mined from the earth is heated strongly in an insufficient supply of air, it produces a solid fuel B which consists mainly of carbon. When another material C obtained from trees is heated in an insufficient supply of air, it produces another solid fuel D which also consists mainly of carbon. Name A, B, C and D.

'A' is Coal.

Explanation

Coal is mined from the earth, as it is produced inside the Earth due to the continuous pressure and heat on the decomposed large dead trees buried deep inside the earth over decades or centuries.

'B' is Coke. 

Explanation

Coke is a grey, hard, and porous fuel with high carbon content and few impurities, made by heating coal in the absence of air so that the volatile components are driven off. It is used as a reducing agent in the extraction of metals from their ores.

'C' is Wood.

Explanation

Wood is obtained from trees.

'D' is Charcoal.

Explanation

Charcoal is prepared by burning wood in a minimal or limited supply of air so that water and other volatile materials (methane, hydrogen, and tar) present in it get removed, and a black substance called charcoal is left behind.