Which feature enforces tag requirements so resources cannot remain untagged across the environment?

Azure Policy is the correct answer because it allows you to define and enforce standards and compliance at scale. You can create policies that require specific tags to be applied to resources during creation or update, preventing untagged resources from being deployed. Azure Advisor provides recommendations for optimizing Azure resources, but it doesn't enforce tagging rules. Azure Automation helps automate tasks and processes, but it's not designed for policy enforcement of resource properties like tags. Azure Monitor collects and analyzes telemetry data from Azure resources, focusing on performance and availability, not policy enforcement.