Choice "D" is correct. The auditor often traces a sample of shipping documents to sales invoices to test completeness of sales.
Choice "a" is incorrect. Subsequent collections are used to verify the existence and valuation of year-end receivables.
Choice "c" is incorrect. Vouching sales orders to supporting documentation provides evidence of the existence of sales, not completeness.
Choice "b" is incorrect. Verifying proper approval of credit memos provides evidence regarding the accuracy of receivables, not the completeness of sales.
