The correct selection is D. The established architecture separates business-unit operations into individual orgs and centralizes enterprise customer data. The new BU should therefore receive its own org for process autonomy and integrate with the customer-data hub so enterprise data governance remains consistent. From a system-design perspective, the decision should minimize unnecessary coupling while preserving clear ownership, scalability, governance, and extensibility. Salesforce architecture is strongest when boundaries reflect real business and technical responsibilities instead of using organizational convenience as the primary design driver. The alternatives are less suitable because they optimize for convenience instead of the long-term system qualities of isolation, reuse, maintainability, and controlled integration. For this scenario, the decisive point is therefore the platform behavior represented by the selected option (D. Use a new Salesforce org for the new BU, and customize integration so that it reads and writes customer information from the customer data org.). Applying that rule consistently keeps the implementation aligned with Salesforce-supported lifecycle practices and makes the resulting change easier to review, validate, and operate across environments.

Study Guide reference: System Design — org strategy; modular architecture; integration topology; data ownership; enterprise governance; scalability.