Materials Requirements Planning $($MRP$)$ is a system designed to help manufacturers ensure that they have the right materials available for production at the right time. Let's evaluate each option:

Ensuring raw materials and subassemblies are available when required to meet the production plan: This is a core function of MRP$.$ It helps in determining what materials are needed and when they are needed to meet production schedules.

Verifying that finished goods are available when needed for delivery to customers: While MRP focuses on planning and scheduling materials for production, ensuring finished goods availability for delivery to customers is typically handled by other processes such as Finished Goods Inventory Management or Order Fulfillment.

Planning the purchasing of raw materials and purchasing or production of subassemblies: This is a key function of MRP$.$ It helps in planning the procurement of raw materials and the production of subassemblies based on the production schedule and inventory levels.

Aggregating sales data and balancing requirements against the capabilities in the supply chain: While MRP uses sales forecasts and production plans to determine material requirements, it doesn't directly involve aggregating sales data or balancing requirements against supply chain capabilities. This task is typically part of Sales and Operations Planning $($S&OP$)$ or Supply Chain Management $($SCM$)$ processes.