Passage Summary: Airlines used to refresh the air in the cabin twice as often as they do now. We know that refreshing air less frequently leads to higher CO2 levels and makes it easier for germs to travel through the air.

Reasoning: The frequency of cabin air replenishment in commercial flights decreased from every 30 minutes to every hour after 1985, and lower replenishment rates are linked to higher carbon dioxide and easier spread of illness.

Analysis: Since this is a Most Strongly Supported question, we must treat the premises as absolute facts and see where they lead. We have a clear 'before and after' comparison: air is now refreshed half as often as it was before 1985. Because the stimulus explicitly links lower replenishment rates to higher CO2 and easier illness transmission, we can infer that modern flights likely have higher CO2 levels and a higher risk of illness spread than pre-1985 flights. Look for an answer choice that draws this direct comparison between the two time periods based on the provided variables.