1.  In the Air Quality Index, the color [ Select ] yellow red purple orange green maroon indicates an air quality that is unhealthy for sensitive groups while the color [ Select ] green purple maroon yellow red orange indicates the most dangerous level of pollutants in the air. 2.  Catalytic converters reduce the amount of [ Select ] ozone carbon dioxide carbon monoxide nitrogen gas in car exhaust. 3.  Hikers on the highest peak of Mt Everest (tallest mountain in the world) are breathing air in the [ Select ] mesosphere troposphere stratosphere exosphere thermosphere . 4.  Which of the following substances is not considered an air pollutant? [ Select ] sulfur dioxide gas sulfur trioxide gas nitrogen gas carbon monoxide nitrogen dioxide 5.  Ozone is considered an air pollutant in the [ Select ] mesosphere stratosphere troposphere thermosphere but is a valuable protective layer in the [ Select ] mesosphere stratosphere troposphere thermosphere . 6.  The layers of the atmosphere that are farther away from the earth has lower overall pressure because they have [ Select ] higher lower amounts of gas molecules. 多重下拉选择题