Last year a chain of fast-food restaurants, whose menu had always centered on hamburger, added its first vegetarian sandwich, much lower in fat than the chain`s other offerings. Despite heavy marketing, the new sandwich accounts for a very small proportion of the chain`s sales. The sandwich`s sales would have to quadruple to cover the costs associated with including it on the menu. Since such an increase is unlikely, the chain would be more profitable if it dropped the sandwich. Which of the following, if true, most seriously weakens the argument?
【选项】Among fast-food chains in general, there has been little or no growth in hamburger sales over the past several years as the range of competing offerings at other restaurants has grown.