What is the MOST cost-effective instance purchasing option to meet these requirements?

Explanations:

Spot Instances are cost-effective but can be interrupted and may not be reliable for steady workloads, making them unsuitable for a long-term application.

Reserved Instances provide a significant discount for committing to a 1-year term, making them the most cost-effective choice for a consistent workload.

On-Demand Instances are flexible but more expensive over time compared to Reserved Instances, making them less cost-effective for long-term use.

Dedicated Hosts are more expensive and designed for specific licensing needs, making them the least cost-effective option for a standard application workload.