A certain credit-card company awards its customers bonus points for using its credit card. Customers can use accumulated points in the purchase of brand name merchandise by mail at prices lower than the manufacturers' suggested retail prices. At any given time, ttherefore, customers who purchase merchandise using the bonus points spend less than they would spend if they purchased the same merchandise in retail stores. Which one of the following is an assumption on which the argument depends? ['The bonus points cannot be used by the creditcard customers in the purchase of brand name merchandise that is not available for purchase in retail stones.', "The credit-card company does not require its customers to accumulate a large number of bonus points before becoming eligible to order merchandise at prices lower than the manufacturers' suggested retail price.", 'The amount credit-card customers pay for shipping the merchandise ordered by mail does not increase the amount customers spend to an amount greater than they would spend if they purchased the same merchandise in retail stores.', "The merchandise available to the company's credit-card customers using the bonus points is frequently sold in retail stores at prices that are higher than the manufacturers' suggested retail prices."]