ANS:C - blast furnace

Pig iron is primarily produced in a blast furnace. In a blast furnace, iron ore (typically hematite or magnetite), coke (a form of carbon), and limestone are combined and heated in a continuous process. The coke acts as both a fuel and a reducing agent, reducing the iron oxide in the ore to metallic iron. The limestone serves as a flux, helping to remove impurities from the iron ore. The resulting product of this process is pig iron, which is a brittle form of iron containing a high concentration of carbon (typically 3-4%), along with other impurities such as silicon, sulfur, and phosphorus. Pig iron is the intermediate product obtained from the blast furnace before it is further processed into wrought iron, steel, or cast iron through additional refining and alloying processes. While electric arc furnaces, cupolas, and open hearth furnaces are also used in iron and steel production, they are typically used for recycling scrap metal or for secondary refining processes rather than for the primary production of pig iron.