A company wants to reduce costs on jobs that can be completed at any time. The jobs are currently run using multiple On-Demand Instances, and the jobs take just under 2 hours to complete. If a job fails for any reason, it can be restarted from the beginning.
Which method is the MOST cost-effective based on these requirements?

A. Purchase Reserved Instances to be used for job execution.
B. Submit a request for a one-time Spot Instance for job execution.
C. Submit a request for a Spot block to be used for job execution.
D. Use a mixture of On-Demand and Spot Instances for job execution.