B．affected the entire eastern half of the United States

　　C．had a very bad effect on health

　　D．existed merely in urban and industrial areas

　　解析：选D　细节理解题。根据文章第一段第一句可知，人们过去认为空气污染只存在于工厂林立的工业区和交通拥挤的大城市当中。故答案选D。

　　5．As to the greenhouse effect, the author .

　　A．shares the same view with the scientists

　　B．is uncertain of its occurrence

　　C．rejects it as being ungrounded

　　D．thinks that it will destroy the world soon

　　解析：选B　推理判断题。根据第一段最后一句中的"If this view is correct and ..."可知，作者并不确定这种观点(来自化石燃料燃烧的二氧化碳会导致温室效应，使全球变暖)是否正确。故答案选B。

　　6．The underlined word "offset" in the second paragraph could be replaced by " "．

　　A．counter­act　　　　　 B．break from

　　C．get along D．communicate

　　解析：选A　词义猜测题。根据画线词所在的句子及其前一句可知，我们不知道这两种可能情况(全球变暖和全球变冷)中的哪种会发生，如果我们足够幸运的话，这两种现象会相互抵消中和，温度依然会保持不变。因此，offset应为"补偿；抵消"之意，故答案选A。

　　7．If the world's temperature lowered just a few degrees .　

　　A．it would not do much harm to life on earth

　　B．it would lead major farming areas to disaster

　　C．particular things would increase greatly in the atmosphere

　　D．seas and oceans would flood many cities

　　解析：选B　细节理解题。根据第二段第二句可知，温度降低几度的话，就会出现类似冰川时代的现象，农业将会变得很困难甚至是不可能了。故答案选B。

　　C

　　Super Bowl Weekend has just ended, and I was very excited for the big game. But I'm not just a fan of the game: I'm a 13­year­old, an offensive guard. I just finished playing my ninth and final season.

Unfortunately, it hasn't come without a fight. During the last two years, they've created rules