A company's production environment runs Amazon EC2 On-Demand Instances continuously from Monday through Saturday. On Sunday the instances must run only 12 hours and cannot tolerate interruptions. The company wants to cost-optimize the environment while meeting these requirements. Which solution is MOST cost-effective?

The correct solution uses Scheduled Reserved Instances (RIs) for the Sunday workload and Standard RIs for the Monday-Saturday workload. Scheduled RIs are designed for instances that run on a predictable schedule, offering significant cost savings over On-Demand for specific time windows, perfectly matching the Sunday requirement. Standard RIs provide the deepest discount for steady-state, continuous usage, which applies to the Monday-Saturday period. Convertible RIs offer flexibility to change instance families, sizes, or operating systems, but they provide a smaller discount than Standard RIs and are not necessary here as the instance types are fixed. Spot Instances are not suitable for the Sunday workload because they can be interrupted, violating the requirement that the instances "cannot tolerate interruptions." Using Spot Instances for the continuous Monday-Saturday workload would also be inappropriate due to the interruption risk for a production environment.