Final answer:
The designated virtual area within each plant where planning occurs for an activity in GCSS-Army's ERP structure is called the MRP Area.
Step-by-step explanation:
The correct answer is B) MRP Area.
In ERP (Enterprise Resource Planning) systems like GCSS-Army, organizational elements are used to represent various units and areas within a plant. In this case, the designated virtual area where planning occurs for an activity is called the MRP (Material Requirements Planning) Area.
MRP areas are used to plan and manage the flow of materials within a plant, enabling efficient production and inventory management. They help in coordinating activities such as material requirements planning, production order scheduling, and resource allocation.