Residents at a retirement community always play card games for two hours, starting at 3: 00 p. m. every afternoon. Although it is clear that the residents take pleasure in this activity, they never continue their games for longer than two hours. Caregivers assume that since card games require great concentration and strain on the elderly residents' eyes, playing for more than two hours would give the residents headaches that would interfere with their ability to play bingo in the evenings. Which of the following, if true, most seriously calls into question the caregivers' explanation? ['Experts have proven that playing card games has tremendous health benefits for elderly people.', 'Residents at the retirement community are served dinner at 5:00 p. m. every evening.', 'Playing bingo takes just as much concentration and causes equal strain on the eyes as card games.', 'Most of the residents at the retirement community rank bingo at the top of their list of favorite activities.']