A company wants to use Amazon EC2 instances.

Amazon EC2 Reserved Instances provide a billing discount in exchange for a one-year or three-year commitment to specified EC2 usage attributes and payment terms. Because the company can commit for one year and expects specific usage, Reserved Instances are the most cost-effective choice among the listed options. A Reserved Instance is not a separate physical instance; its billing benefit is applied to qualifying running EC2 instances that match the reservation’s attributes. Dedicated Hosts provide an entire physical host for one customer and are appropriate for host-level compliance or licensing requirements, but those requirements are not stated here. Spot Instances can provide larger discounts by using spare EC2 capacity, but AWS can interrupt them, and the question describes a predictable committed workload rather than an interruption-tolerant workload. On-Demand Instances require no long-term commitment and are appropriate for short-term, irregular, or unpredictable workloads, but their normal usage price is higher than a matching Reserved Instance commitment. Although AWS also offers Savings Plans, they are not included in the options. Therefore, Reserved Instances are the intended answer for a one-year EC2 usage commitment.