第一节 完形填空（共15小题；每小题2分，满分30分）阅读下面短文，掌握其大意，然后从1~15各题所给的a、b、c和d项中，选出最佳选项，并在答题卡上将该项涂黑。 many of the world's pollution problems have been caused by the crowding of large groups of people into the cities. supply for the needs of the people leads to further 1 by industry. if the rapid increase of world 2 continues at the present rate, there may be much greater 3 to human beings. some scientists 4 of the increase in numbers of people as "population pollution''. about 2,000 years ago, the world population was about 250 million. it 5 a billion in 1850. by 1930 the population was two billion. it is now six billon. it is 6 to double by the year 2020. if the population 7 to grow at the same rate, there will be 25 billion people in the 8 a
