A lockbox is a: A. special safe used by a firm for overnight storage of any cash or undeposited checks. B. special safe used by a firm that can only be opened at prespecified times of the day. C. box located in a bank's vault that is rented by a firm and used to hold unprocessed checks. D. special post office box which can only be opened by prespecified postal inspectors for direct delivery to the addressee. E. post office box strategically located so that a firm's receivables can be collected faster.