The correct answer is: A. Refining
Pig iron is a type of iron that is produced in a blast furnace. It is a very impure form of iron, containing about 4% carbon and other impurities. Wrought iron is a type of iron that is much more pure than pig iron. It is produced by a process called refining, which removes the impurities from pig iron.
Pudding is a term used to describe the process of heating pig iron until it is molten. Shingling is a term used to describe the process of hammering molten pig iron into thin sheets.
Neither pudding nor shingling are necessary steps in the production of wrought iron. Wrought iron can be produced by refining pig iron without either of these steps.
Therefore, the correct answer is: A. Refining