AWS CloudTrail is a service that enables governance, compliance, and operational and risk auditing of an AWS account. It logs, continuously monitors, and retains account activity related to actions across an AWS infrastructure.

For auditing purposes:

CloudTrail records AWS API calls made in the account, including details about who made the request, the services used, the actions performed, and the response elements returned by AWS.

This information is critical for understanding user activity, detecting anomalous behavior, and performing security analysis and compliance auditing.

Why other options are not suitable:

A. AWS Config: AWS Config provides a detailed view of the configuration of AWS resources, including how resources are related and their compliance with internal policies, but it does not provide a comprehensive audit trail of user actions.

B. Amazon Rekognition: A service for image and video analysis, not relevant to auditing AWS account activity.

D. Amazon SNS: A notification service for sending alerts and messages, not used for auditing purposes.