The following four questions are taken from an internal control questionnaire. For each question, state (a) one test of controls procedure you could use to find out whether the control technique was really functioning and (b) what error or fraud could occur if the question were answered "no" or if you found the control was not effective. Required: 1. Are blank sales invoices available only to authorized personnel? 2. Are sales invoices prenumbered and are all numbers accounted for? a. Inspect documents for evidence that the billing department supervisor matches prenumbered shipping documents with entries in the sales journal b. Not all accounts receivable have been recorded 3. Are sales invoices checked for the accuracy of quantities billed? Prices used? Mathematical calculations? a. 4. Are the duties of the accounts receivable bookkeeper separate from all cash functions? a. 5. Are customer accounts regularly balanced with the control account? 6. Do customers receive a monthly statement even when the ending balance on the account is zero?