Which tool should an Azure administrator use to allow only a predefined set of virtual machine sizes in production?

Azure Policy is the correct tool because it enforces organizational standards and assesses compliance at scale. You can create a policy definition that restricts the allowed virtual machine sizes and assign it to your production environment. If a user tries to deploy a VM with an unapproved size, Azure Policy will block the deployment. Azure Advisor provides recommendations for optimizing resources, but doesn't enforce rules. Azure Monitor collects and analyzes telemetry data, focusing on performance and availability, not resource governance. Azure Blueprints define a repeatable set of Azure resources that implement and adhere to standards, but Azure Policy is the specific enforcement mechanism for resource properties like VM sizes.