题目选项分析

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】Many of the people who eat at the chain's restaurants also eat at the restaurants of competing chains and report no strong preference among the competitors.