A financial service company is running distributed computing software to manage a fleet of 20 servers for their calculations. There are 2 control nodes and 18 worker nodes to run the calculations. Worker nodes can be automatically started by the control nodes when required. Currently, all nodes are running on demand, and the worker nodes are used for approximately 4 hours each day.
Which combination of actions will be MOST cost-effective? (Choose two.)

A. Use Dedicated Hosts for the control nodes.
B. Use Reserved Instances for the control nodes.
C. Use Reserved Instances for the worker nodes.
D. Use Spot Instances for the control nodes and On-Demand Instances if there is no Spot availability.
E. Use Spot Instances for the worker nodes and On-Demand Instances if there is no Spot availability.