Final answer:
The auditor would select a sample of transactions from the sales invoice file to determine the effectiveness of the internal control system in minimizing errors of failure to invoice a shipment. Thus, the correct option is D.
Step-by-step explanation:
The answer is D) sales invoice file. To determine whether the system of internal control operated effectively to minimize errors of failure to invoice a shipment, the auditor would select a sample of transactions from the sales invoice file. This file contains the actual invoices generated for each shipment, and reviewing a sample of these invoices allows the auditor to assess whether any errors or omissions occurred in the invoicing process.