Hoping to attract new customers, World Air airline is planning to offer its World Flights bonus plan for customers who fly more than six flights in any year. World Flights will entitle each customer who qualifies for one free domestic, round trip flight per year. More than 25% of World Air customers will qualify for this plan. Even with these free flights, World Air expects to increase profits substantially.

Which of the following, if true, would most seriously weaken the above argument?

【选项】World Air primarily flies domestically; they have only a limited number of international routes.