The correct answer is C. Process costing.
Process costing is a method of accounting for the costs of production in industries that manufacture products in large quantities through a continuous process. The costs of materials, labor, and overhead are accumulated by department or process and then assigned to units of product as they are produced.
Job costing is a method of accounting for the costs of production in industries that manufacture products in small quantities or batches. The costs of materials, labor, and overhead are accumulated by job and then assigned to units of product as they are completed.
Operating costing is a method of accounting for the costs of production in industries that provide services rather than products. The costs of labor, materials, and overhead are accumulated by department or function and then assigned to services as they are provided.
In the question, the raw material is to pass certain stages, before it is converted into finished goods. This indicates that the industry is one that manufactures products in large quantities through a continuous process. Therefore, the correct method of costing is process costing.