A research team has found that people who fall asleep in closed environments are more likely to wake up more frequently and feel poorer sleep quality. Therefore, some people think that closing the doors and windows at bedtime will reduce sleep quality. Which of the following is true that would most weaken the above conclusion? ['The research group surveyed mostly young people.', 'People with poor sleep quality prefer to close the doors and windows to sleep.', 'Closed doors and windows can affect indoor air quality and affect sleep.', 'Window opening at night is not suitable for all rooms due to security, warmth, etc.']