A company accepts orders for customers in their enterprise resource planning (ERP) system that must...

When integrating external systems with Salesforce and creating records that need to be associated with existing Salesforce records based on an external ID, Salesforce provides the ability to reference an external ID field in a related object directly within a create or update call.

Option A is correct because the upsert operation can be used to either insert new records or update existing ones. By specifying the external ID field (ENF_Customer_ID__c) for the Account relationship, the system will automatically link the Order__c record to the correct Account based on the external ID provided by the ERP system.

Options B, C, and D are incorrect because they do not specifically utilize the capability of referencing an external ID to associate records during an integration process.