Until 1985 all commercial airlines completely replenished the cabin air in planes in flight once every 30 minutes. Since then the rate has been once every hour. The less frequently cabin air is replenished in a plane in flight, the higher the level of carbon dioxide in that plane and the easier it is for airborne illnesses to be spread. Which one of the following is most strongly supported by the information above? ['In 1985 there was a loosening of regulations concerning cabin air in commercial airline flights.', 'In 1980 the level of carbon dioxide in the cabin air on a two-hour commercial airline flight was lower than it is today on a similar flight.', 'People who fly today are more likely to contract airborne illnesses than were people who flew prior to 1985.', 'Low levels of carbon dioxide in cabin air make it impossible for airborne illnesses to spread.']