The correct option is Soft delete for Azure Files.

This feature retains deleted files and directories for a configurable retention period so a deleted file can be restored without needing a point in time snapshot or a backup. When a file is deleted it is retained by the service and you can undelete it through the portal PowerShell or CLI as long as the retention period has not expired.

Azure File Sync is incorrect because it synchronizes and tiers files between on premises servers and Azure and it does not provide the immediate soft delete retention that allows simple undelete at the file level in the storage account.

Azure Files snapshots is incorrect because snapshots are point in time copies of a share that must exist before a deletion to be useful for recovery and they are not the same as the automatic retention that soft delete provides.

Azure File share backup is incorrect because Azure Backup can restore files from backups under backup policies but it is a separate backup solution and not the lightweight soft delete retention that directly enables quick undelete of a deleted file.

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