单选题 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.

单选题 Which of the following is TRUE according to the passage?

【正确答案】 D

【答案解析】解析：事实细节题。信息定位于第一段和第二段。段中提到，ground—level ozone地水准(基态)臭氧能影响人的健康，也会损害作物和其他蔬菜。起保护作用的有益臭氧出现在平流层。有害臭氧形成在地表，是由一些污染物形成的。选项A、B、C与上面提及内容相悖。选项D与首段第一句信息一致，故答案为D。

单选题 It can be learned from the passage that______.

【正确答案】 C

【答案解析】解析：事实细节题。文章第一段末句提及有益臭氧能保护地球上的生物不受有害太阳射线的伤害。选项A和B与以上信息相悖。第二段末句提及美国的北部和西北部的臭氧季长达一年(lasts nearlythe entire year)，但并没有提及是最长的。选项D说法不准确。选项C的内容是第二段中“Ozonepollution is a concern during the summer months”的同义转述。故答案为C。