The correct answer is: A. coal and limestone
Coal and limestone are the two most important minerals of Assam. Coal is a fossil fuel that is used to generate electricity and power industries. Limestone is a sedimentary rock that is used in the construction industry and to make cement.
Petroleum is also an important mineral of Assam, but it is not as abundant as coal and limestone. Petroleum is a fossil fuel that is used to make gasoline, diesel fuel, and other products.
Copper and mica are not as important as coal, limestone, and petroleum. Copper is a metal that is used to make electrical wires and other products. Mica is a mineral that is used in electrical insulation and other products.
Manganese, gold, and quartzite are not as important as coal, limestone, petroleum, copper, and mica. Manganese is a metal that is used in steelmaking. Gold is a precious metal that is used in jewelry and other products. Quartzite is a type of sandstone that is used in construction.