Smith Manufacturing Company's accounts receivable clerk has a friend who is also Smith's customer. The accounts receivable clerk, on occasion, has issued fictitious credit memorandums who has friend for goods supposably returned (these returns did not exist). the most effective control for preventing this activity is to: a. prenumber and account for all credit memorandums b. require receiving reports to support all credit memorandums before they are approved c. have the sales department independent of the accounts receivable Department d. mail monthly statements to the customer