Which AWS service or tool provides real-time monitoring of AWS resources and applications?

Amazon CloudWatch is the correct answer because it is a monitoring and observability service that provides real-time data and actionable insights for AWS resources, applications, and on-premises servers. It collects monitoring and operational data in the form of logs, metrics, and events, and allows users to set alarms, visualize data, and automate actions based on predefined thresholds. AWS Trusted Advisor is incorrect because it provides recommendations for optimizing performance, security, cost, and fault tolerance, not real-time monitoring. AWS CloudTrail is incorrect because it records API calls and events for auditing and governance, not real-time performance monitoring. AWS Cost Explorer is incorrect because it allows you to visualize, understand, and manage your AWS costs and usage over time.