An internal auditor is investigating the performance of a division with an unusually large increase in sales, gross margin, and profit. Assume that the analysis shows unusually high sales and gross margin during the months of November and December and the internal auditor wishes to investigate further. Which of the following engagement procedures will be most effective in analyzing whether fraudulent sales may have been recorded? A. Take a sample of shipping documents and compare them with the related sales invoices, noting that all items were properly billed. B. Confirm accounts receivable with large customers. C. Perform an analytical review comparing sales and gross margin with the previous 10 months and the first month of the following year. D. Use regression analysis techniques for the first 10 months to estimate the sales and cost of goods sold for the last 2 months.