A wholesaling firm has a computerized billing system. Because of a clerical error while entering information from the sales order, one of its customers was billed for only three of the four items ordered and received.
Which of the following controls could have prevented, or resulted in prompt detection and correction, of this situation?

a) Matching line control counts produced by the computer with predetermined line control counts.
b) Periodic comparison of total accounts receivable per accounts receivable master file with total accounts receivable per accounts receivable control account.
c) Prenumbered shipping documents together with a procedure for follow-up any time there is not a one-to-one relationship between shipping documents and sales invoices.
d) A completeness check that does not allow a sales invoice to be processed if key fields are blank.