A recent epidemiological study found that businesspeople who travel internationally on business are much more likely to suffer from chronic insomnia than are businesspeople who do not travel on business. International travelers experience the stresses of dramatic changes in climate, frequent disruption of daily routines, and immersion in cultures other than their own, stresses not commonly felt by those who do not travel. Thus, it is likely that these stresses cause the insomnia. Which one of the following would, if true, most strengthen the reasoning above? ['Businesspeople who already suffer from chronic insomnia are no more likely than businesspeople who do not to accept assignments from their employers that require international travel.', 'Experiencing dramatic changes in climate and disruption of daily routines through international travel can be beneficial to some people who suffer from chronic insomnia.', 'Most international travel for the sake of business occurs between countries with contiguous borders.', 'Some businesspeople who once traveled internationally but no longer do so complain of various sleep-related ailments.']