Final answer:
Lot Size (c) is the field that determines the frequency and size of planned orders. It refers to the amount of inventory ordered or produced in one go, influencing how often and how large the orders should be.
Step-by-step explanation:
The field that controls the frequency and size of planned orders in inventory management is the Lot Size (c). The Lot Size refers to the quantity of an item that is ordered from the supplier or produced in a single production run. This affects both how often orders are placed and how large each order is.
Safety Stock is a buffer of inventory used to prevent stockouts due to variable demand or supply delays. The Reorder Point is the level of inventory at which a new order should be placed, and Lead Time is the duration between placing an order and receiving it. These factors are important in inventory management, yet they are not directly responsible for determining the frequency and size of orders; that's primarily the role of Lot Sizes.