Which Azure feature can automate shutting down unused VMs to reduce costs?

Azure Automation is the correct choice because it provides capabilities for process automation, including scheduling tasks like starting or stopping virtual machines. This allows you to define policies to automatically shut down VMs during off-hours, significantly reducing compute costs for resources that aren't actively in use. Azure Monitor is used for collecting, analyzing, and acting on telemetry data from your Azure and on-premises environments, not for direct resource management. Azure Arc extends Azure management to resources outside of Azure, like on-premises servers or other cloud environments, but doesn't inherently automate cost-saving shutdowns. Azure Sentinel is a cloud-native Security Information and Event Management (SIEM) solution for security analytics and threat intelligence.