2. 外语
  3. Ground-level ozone is an air pollutant that causes human health problems even at very low levels. It also damages crops and othe

Ground-level ozone is an air pollutant that causes human health problems even at very low levels. It also damages crops and othe

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问题     Ground-level ozone is an air pollutant that causes human health problems even at very low levels. It also damages crops and other vegetation. It is a key ingredient of urban smog. "Good ozone" occurs naturally in the stratosphere approximately 10 to 30 miles above the earth’s surface and forms a layer that protects life on earth from the sun’s harmful rays.
    "Bad ozone" is formed in the earth’s lower atmosphere, near ground level, when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the present of sunlight. Ozone pollution is a concern during the summer months when the weather conditions needed to form ground-level ozone — lots of sun, hot temperatures — normally occur. The length of ozone season varies from one area of the United States to another. Southern and southwestern states may have an ozone season that lasts nearly the entire year.
    Ozone can irritate lung airways and cause inflammation much like sunburn. Other symptoms include wheezing, coughing, pain when taking it deep breath, and breathing difficulties during exercise of outdoor activities. People with respiratory problems are most vulnerable, but even healthy people who are active outdoors can be affected when ozone levels are high. Repeated exposure to ozone pollution for several months may cause permanent lung damage. Anyone who spends time outdoors in the summer is at risk, particularly children and other people who are active outdoors. Even at very low levels, ground-level ozone triggers a variety of problems including aggravated asthma, reduced lung capacity, and increased susceptibility to respiratory illnesses like pneumonia and bronchitis.
    Ozone damage can occur without any noticeable signs. People who love in areas where ozone levels are frequently high may find that their initial symptoms go away overt time — particularly when exposure to high ozone levels continues for several days. Ozone continues to cause lung damage even when the symptoms have disappeared.
We can see that the passage is mainly about______.
选项 A、good ozone and its function of protecting people
B、ozone pollution and its effects on people’s health
C、the measures mat Southern states of the U. S. should take against ozone pollution
D、how people with respiratory problems should protect themselves from ozone pollution
答案B
解析 主旨思想题。结合文章大意可知，本文主要讲述了臭氧污染对人类健康的影响及其形成。选项C和D在文中没有提及，选项A不是全文的重点。选项B符合文意。故答案为B。
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