A level production strategy is a manufacturing strategy where a company produces a fixed number of products at a fixed rate1. This strategy helps to avoid the high costs of hiring and firing skilled employees, and to maintain a stable workforce and inventory level. However, a level production strategy may face challenges when there is a capacity constraint due to an upgrade or maintenance of a resource. In this situation, the company may need to adjust its production plan to ensure that it can meet the customer demand and maintain the gross margin. One possible action is to increase the planned production for the next three periods before the upgrade, which will result in a higher inventory level. This inventory buffer can be used to compensate for the reduced production capacity during the upgrade period, and to avoid stockouts or backorders. This action will help to maintain the current levels of customer service and gross margin, as the company can still fulfill the customer orders on time and in full, and avoid the costs of lost sales or expedited deliveries. Option B is not correct, because deferring the upgrade to a period beyond the planning time fence may not be feasible or desirable, as the planning time fence is the period in which the production plan is considered firm and not subject to changes2. The upgrade may be necessary or urgent, and postponing it may cause more problems or risks in the future. Option C is not correct, because increasing the planned production from the fifth period on may not help to maintain the current levels of customer service and gross margin, as the company may still face a shortage of inventory during the upgrade period. Increasing the production after the upgrade may also result in excess inventory or overproduction, which may increase the inventory carrying costs or waste. Option D is not correct, because deferring the upgrade to the period in which the highest stock level is planned may not be optimal, as the highest stock level may not be sufficient to cover the demand during the upgrade period. Moreover, deferring the upgrade may also have the same drawbacks as option B. References: 1 Guide to Level Production Strategy - Welp Magazine 3 2 Planning Time Fence | SAP Help Portal 4