When a user wants to utilize their existing per-socket, per-core, or per-virtual machine software licenses...

The correct answer is C because Dedicated Hosts are Amazon EC2 instances that are required when a user wants to utilize their existing per-socket, per-core, or per-virtual machine software licenses for a Microsoft Windows server running on AWS. Dedicated Hosts are physical servers that are dedicated to a single customer. Dedicated Hosts allow customers to use their existing server-bound software licenses, such as Windows Server, SQL Server, and SUSE Linux Enterprise Server, subject to their license terms. The other options are incorrect because they are not Amazon EC2 instances that are required when a user wants to utilize their existing per-socket, per-core, or per-virtual machine software licenses for a Microsoft Windows server running on AWS. Spot Instances are spare Amazon EC2 instances that are available at up to 90% discount compared to On-Demand prices. Spot Instances are suitable for stateless, fault-tolerant, and flexible workloads that can recover from interruptions easily. Dedicated Instances are Amazon EC2 instances that run on hardware that is dedicated to a single customer, but not to a specific physical server. Dedicated Instances do not allow customers to use their existing server-bound software licenses. Reserved Instances are Amazon EC2 instances that are reserved for a specific period of time (one or three years) in exchange for a lower hourly rate. Reserved Instances are suitable for steady-state or predictable workloads that run for a long duration. Reserved Instances do not allow customers to use their existing server-bound software licenses. Reference: Dedicated Hosts, Amazon EC2 Instance Purchasing Options