The correct answer is A. bauxite. Bauxite is the most important ore of aluminium because it is the only ore that contains bauxite, which is the main source of aluminium. Bauxite is a clay-like mineral that is found in tropical and subtropical regions. It is the most abundant ore of aluminium, and it is the only ore that can be economically mined. Bauxite is a mixture of several minerals, including gibbsite, boehmite, and diaspore. These minerals are all aluminum oxides, and they are the main source of aluminum in bauxite. Bauxite is mined by open-pit mining, and it is then processed to remove the impurities. The resulting product is called alumina, which is the main raw material for aluminum production.
Magnetite is an iron ore, and it is not a source of aluminum. Haematite is also an iron ore, and it is not a source of aluminum. Monazite is a rare earth mineral, and it is not a source of aluminum.