Final answer:
The most likely procedure that would not be an internal control activity to reduce the risk of errors in the billing process.
Step-by-step explanation:
The correct answer is d. Reconciling the control totals for sales invoices with the accounts receivable subsidiary ledger. This is because reconciling the control totals with the subsidiary ledger is a process of ensuring that the totals match and it doesn't directly reduce the risk of errors in the billing process. It is more of a verification step rather than an internal control. The other options, a, b, and c, are all internal control activities that help reduce the risk of errors in the billing process.