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  3. A country is said to become more urbanized as its cities grow in number, its urban populations increase in size, and the proport

A country is said to become more urbanized as its cities grow in number, its urban populations increase in size, and the proport

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问题     A country is said to become more urbanized as its cities grow in number, its urban populations increase in size, and the proportion of its population living in urban areas rises. The degree of urbanization varies across the world but generally reflects the wealth of individual countries. The rich, industrialized countries tend to be the most highly urbanized. In the Netherlands, for example, 89 percent of the population is urban, compared to only 13 percent in Ethiopia, a much poorer country.
    In recent history, the degree of urbanization has been relatively low in Africa and Asia compared to Europe and North America. However, as a result of large-scale migration from rural areas and a natural increase in the urban populations themselves, the populations of cities in the developing world have been growing rapidly. The population of Cairo, for example, has tripled in the last 40 years, and more than half of Africa’s people are expected to be living in cities by 2020. Similarly, the urban share of the population in China has risen from about one in five in 1960 to nearly half today.
    One of the most noticeable features of urban growth in the 20th century has been the rapid increase in the number of very large cities. Before 1800, cities with more than a million inhabitants were rare. Since then, however, the number of such cities has risen steadily. In 1900 there were at least 13 cities with more than a million inhabitants, and by 1950 the number had grown to 68. By 2000 there will be at least 250 cities of more than a million--many of which will be in Asia, especially in India and China.
    Even a city of a few million people is dwarfed by the urban giants with populations exceeding 10 million. According to various estimates, there may be 20 or more of these gigantic metropolitan areas already. Most are in Asia: Tokyo, Seoul, Osaka, Shanghai, Mumbai (Bombay), Beijing, Calcutta, Jakarta, Tianjin, Karachi, Delhi, and Manila. The other giants are New York, Sao Paulo, Mexico City, Los Angeles, Moscow, Buenos Aires, Rio de Janeiro, and Cairo. In coming years, explosive growth in cities of the developing world such as Lagos and Santa Fe de Bogotá will almost certainly propel them into this group. By the year 2020, several cities are expected to have populations of more than 20 million.
    Such large concentrations of people pose immense environmental problems. In Mexico City, for example, one-quarter of the population has no access to running water, and one in five houses is not connected to the sewerage system. Located in a valley, the city suffers so badly from air pollution from motor vehicles that the city center must periodically be closed to traffic. Mexico City’s problems are replicated in most other large cities in the developing world, and to a lesser degree in the large cities of industrialized countries as well.
It can be learned from the last paragraph that ______.
选项 A、motor vehicles are the main cause for air pollution in Mexico
B、there’s a shortage of water supply and houses in Mexico
C、air pollution is serious in Mexico because of its location
D、urbanization leads to environmental problems in both developing and developed countries
答案D
解析
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