A company has an asynchronous nightly process that feeds the results to a data warehouse system for weekly and monthly reporting. The process is running on a fleet of Amazon EC2 instances. A SysOps Administrator has been asked to identify ways to reduce the cost of running this process.
What is the MOST cost-effective solution?

A. Use On-Demand EC2 instances in an Auto Scaling group
B. Use Spot Instances to bid for the EC2 instances
C. Use Reserved Instances to ensure the capacity
D. Put the EC2 instances in a placement group