Answer: Amazon CloudWatch

## Explanation **Amazon CloudWatch** is the correct answer because it provides comprehensive monitoring and logging capabilities across AWS services. CloudWatch can collect and track metrics, collect and monitor log files, and set alarms. It offers a complete audit trail by: - **CloudWatch Logs**: Collects log data from AWS services and applications - **CloudWatch Events (now EventBridge)**: Provides a real-time stream of system events that describe changes in AWS resources - **Comprehensive monitoring**: Tracks usage and performance across multiple AWS services **Why the other options are incorrect:** - **AWS Trusted Advisor (A)**: This service provides recommendations to optimize AWS infrastructure for cost optimization, performance, security, and fault tolerance, but it does not provide a complete audit trail of service usage. - **Amazon EC2 instance usage report (B)**: This only provides usage data specifically for EC2 instances and does not cover all AWS services used within an account. For a complete audit trail of ALL AWS services used within an account, Amazon CloudWatch is the appropriate service as it can monitor and log activities across the entire AWS environment.

Author: Ritesh Yadav