Which combination of actions will meet these requirements?

Explanations:

EC2 Instance Savings Plans provide a cost-effective way to purchase compute capacity for long-term workloads. Since the control nodes must run 24/7, purchasing Savings Plans for the control nodes will reduce costs by committing to consistent usage.

Dedicated Hosts are more expensive compared to other options like Savings Plans or On-Demand Instances. They are typically used for workloads requiring physical servers for compliance, but not necessary for the control nodes in this scenario.

Reserved Instances provide a cost-effective way to reserve compute capacity but are less flexible than Spot Instances. Since task nodes run only 4 hours a day, the inflexibility of Reserved Instances makes them less optimal for cost-saving in this case.

Spot Instances are suitable for flexible workloads but are not ideal for control nodes that must be always available. If the Spot Instances for control nodes are terminated, the system would be disrupted.

Spot Instances are ideal for task nodes since they run only 4 hours a day and can tolerate interruptions. Using Spot Instances can significantly reduce costs, with On-Demand Instances used as a fallback if Spot availability is low.