The correct answer is A, All Upfront Reserved Instances. This option requires a one-time upfront payment for the entire reservation term, which in this case is 1 year. It provides the largest discount compared to On-Demand Instance pricing, making it the most cost-effective choice for a workload that needs to run continuously for a year without interruptions. The other options, such as Partial Upfront Reserved Instances, Dedicated Instances, and On-Demand Instances, do not offer the same level of cost savings or may not guarantee the required level of service availability.