Which of the following about air pollution does the passage suggest？
A. Further attempts to reduce emissions from gasoline-fueled vehicles will nor help lower urban air pollution levels.
B. Attempts to reduce the pollutants that an individual gasoline-fueled vehicle emits have been largely unsuccessful.
C. Few serious attempts have been made to reduce the amount of pollutants emitted by gasoline fueled vehicles.
D. Pollutants emitted by gasoline-fueled vehicles are not the most critical source of urban air pollution.
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