Your company is incurring unexpected charges from idle virtual machines left running. Which service can help identify and shut down unused resources?

Azure Advisor is the correct answer because it provides personalized recommendations to optimize your Azure deployments. It analyzes your resource configuration and usage telemetry, then suggests ways to improve high availability, security, performance, operational excellence, and cost. In this scenario, Advisor would identify idle virtual machines and recommend shutting them down to reduce costs. Azure Policy helps enforce organizational standards and assess compliance, but it doesn't proactively identify idle resources. Azure Lighthouse allows service providers to manage Azure resources across multiple tenants, which is unrelated to cost optimization for idle resources. Azure Monitor collects and analyzes telemetry from your Azure resources, but it primarily provides monitoring and alerting, not direct recommendations for cost savings from idle resources like Advisor does.