The correct answer is: D. both B and C
Direct manufacturing labor cost is included in both prime costs and conversion costs.
Prime costs are the costs of direct materials and direct labor. Direct materials are the materials that can be physically traced to the finished product. Direct labor is the labor that is directly involved in the production of the finished product.
Conversion costs are the costs of converting direct materials into finished products. Conversion costs include direct labor and manufacturing overhead. Manufacturing overhead is the indirect costs of production, such as indirect labor, indirect materials, and factory overhead.
Therefore, direct manufacturing labor cost is included in both prime costs and conversion costs.