Using clean-coal technologies to "repower" existing factories promises ultimately a substantial reduction of polluting emissions, and will affect the full range of pollutants implicated in acid rain. The strategy of using these technologies could cut sulfur dioxide emissions by more than 80 percent and nitrogen oxide emissions by more than 50 percent. The emission of a smaller quantity of nitrogen pollutants would in turn reduce the formation of noxious ozone in the troposphere. Which one of the following statements is an inference that can be drawn from the information given in the passage? ['Noxious ozone is formed in factories by chemical reactions involving sulfur dioxide.', 'Twenty percent of the present level of sulfur dioxide emissions in the atmosphere is not considered a harmful level.', 'The choice of technologies in factories could reduce the formation of noxious ozone in the troposphere.', 'Sulfur dioxide emissions are the most dangerous pollutants implicated in acid rain.']