An application running on Amazon EC2 must remain available and operational continuously for three or more years. Which EC2 purchasing option should the company choose to obtain a discount on instance pricing?

Reserved Instances (RIs) are the correct choice because they offer significant discounts (up to 75%) compared to On-Demand pricing for instances committed to a 1-year or 3-year term. This aligns perfectly with the requirement for an application needing to run continuously for three or more years. Spot Instances are unsuitable as they are for fault-tolerant workloads that can tolerate interruptions, which is not the case for an application needing continuous availability. On-Demand Instances offer no long-term discount and are more expensive for continuous, predictable workloads. EC2 Fleet is a feature for launching and managing a fleet of EC2 instances across different instance types, Availability Zones, and purchasing options, but it is not a purchasing option itself that provides a discount for long-term commitment.