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. 1. Are sales invoices pre-numbered and are all numbers accounted for? 2. Are voucher packages marked upon payment? 3. Are the duties of the accounts receivable bookkeeper separate from all cash functions? 4. Are invoices matched to receiving reports and purchase orders