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Must Be True. The correct answer choice is (E)
This is a rather complex stimulus dealing with the potentially beneficial effects of repowering factories with clean-coal technologies. The primary effect discussed is the reduction of pollutants involved in acid rain formation, specifically sulfur dioxide and nitrogen oxide. We are then told in the final sentence that a reduction in the amount of emitted nitrogen pollutants would reduce noxious oxide in the troposphere. The only real inference to be drawn from this seems to be a near restatement: clean-coal technologies can reduce the amount of certain substances in the troposphere.
While this stimulus does provide us with some useful information about the connection between clean-coal technologies, polluting emissions, and some specific chemical pollutants, what is perhaps more important is what this stimulus does not tell us. That is, we really do not know much about how these how these chemicals are formed or emitted, what role they play in the formation of acid rain, or even how clean-coal technologies will be implemented to counteract this pollution. So be particularly wary of answer choices that go beyond the information provided in the stimulus and attempt to make assumptions about the details provided.
Answer choice (A): There is no way to know that sulfur dioxide emissions are the most dangerous pollutants implicated in acid rain. While they seem to play a part in acid rain formation, to compare them to all other pollutants involved is impossible.
Answer choice (B): We do not have any information on specifically how noxious ozone is formed, and what little information we do have connects noxious ozone to nitrogen pollutants/nitrogen oxide, not sulfur dioxide. Further, the stimulus discusses noxious ozone formed in the troposphere, while this answer choice deals with the formation of noxious ozone in factories.
Answer choice (C): While the stimulus does state that it may be possible to cut sulfur dioxide emissions by more than 80 percent, there is no way to conclude anything about how harmful the remaining 20 percent would be. The notion of what constitutes “harm” or a “harmful level” is never addressed in the stimulus.
Answer choice (D): A substantial reduction of polluting emissions seems to be a possible benefit of using clean-coal technologies in factories, but to conclude that this will be achieved by redesigning factories is an assumption that cannot be known. Plus, the stimulus discusses redesigning existing factories whereas this answer references "new" factories, which we do not know anything about.
Answer choice (E): This is the correct answer choice. As mentioned above, the connection in the stimulus is that choosing to use certain technologies (clean coal) could reduce the formation/amount of noxious ozone in the troposphere.