A company must save medical trial results in an Amazon S3 repository where a few scientists can add new files and all other users have read-only access. No user may modify or delete any files, and every file must be retained for at least 1 year from its creation date. Which solution meets these requirements?

The correct option is S3 Object Lock in compliance mode with a retention period of 365 days. Compliance mode prevents any user, including the root user, from deleting or overwriting an object until the retention period expires, ensuring data immutability for the required year. A legal hold is used for indefinite retention based on legal discovery, not a fixed period. IAM roles and bucket policies can control access but don't prevent deletion by authorized users or ensure immutability. An AWS Lambda function tracking hashes could detect modifications but wouldn't prevent them or enforce retention.