The correct approach is to assign the auditor the IAM role roles/logging.privateLogViewer and direct them to review logs for changes to Cloud IAM policy. This role grants the necessary permissions to view both Admin Activity and Data Access logs, ensuring a comprehensive audit. Google recommends this method for external audits to maintain security and privacy standards.

• Option A is incorrect because exporting logs to Cloud Storage is unnecessary when direct access is provided, and it overlooks the need to review IAM policy changes.
• Option C is incorrect due to the unnecessary complexity of a custom role when a predefined role suffices.
• Option D is incorrect for similar reasons to Option A, with the added redundancy of exporting logs.