The correct answer is: a) Coal.
Open-cast mining is a surface mining technique in which minerals and ores are extracted from the earth by removing the overlying soil and rock. It is the most common form of mining for coal, iron ore, and other minerals that are found close to the surface.
Open-cast mining is a relatively inexpensive and efficient way to extract minerals, but it can have a significant impact on the environment. The process of removing the overlying soil and rock can damage ecosystems and pollute water supplies. In addition, open-cast mines can leave large scars on the landscape.
Limestone is a sedimentary rock that is formed from the accumulation of calcium carbonate. It is a common building material and is also used in the production of cement, lime, and other products. Limestone is typically mined using underground mining methods, which are less disruptive to the environment than open-cast mining.
Petroleum is a fossil fuel that is formed from the remains of ancient organisms. It is a valuable resource that is used to produce gasoline, diesel fuel, and other products. Petroleum is typically extracted from the earth using deep wells.
Iron ore is a mineral that is used to produce iron. Iron is a valuable metal that is used to make a variety of products, including steel, cars, and appliances. Iron ore is typically mined using open-cast mining methods.