Which AWS service provides auditing of API activity across an AWS account?

AWS CloudTrail is the correct answer because it provides a record of actions taken by a user, role, or an AWS service in AWS. It logs API calls made to AWS services, allowing for auditing, security analysis, and troubleshooting. Amazon Inspector is an automated security assessment service that helps improve the security and compliance of applications deployed on AWS. AWS WAF (Web Application Firewall) helps protect web applications from common web exploits. AWS Config enables you to assess, audit, and evaluate the configurations of your AWS resources, but it doesn't log API activity directly.