Final answer:
EC2 Capacity reservations should be used when you have predictable, steady-state workloads.
Step-by-step explanation:
EC2 Capacity reservations payment provides two different payment options: On-Demand and Reserved Instances.
For the given options (A, B, C, and D), option C: When you have predictable, steady-state workloads, is the most appropriate scenario to use EC2 Capacity reservations.
This is because EC2 Capacity reservations allow you to reserve capacity in advance for a specific instance type in a specified Availability Zone, which is beneficial when you have workloads that consistently require a certain amount of capacity.