单项选择题

Faster than ever before, the human world is becoming an urban world. By the millions they come, the ambitious and the down-trodden of the world drawn by the strange magnetism of urban (41) . For centuries the progress of civilization has been (42) by the rigid growth of cities. Now the world is (43) to pass a milestone: more people will live in urban areas than in the countryside.
Explosive population growth (44) a torrent of migration from the countryside are creating cities that dwarf the great capitals of the past. By the (45) of the century, there will be fifty-one "megacities" with populations of ten million or more. Of these, eighteen will be in (46) countries, including some of the poorest nations in the world. Mexico City already (47) twenty million people and Calcutta twelve million. According to the World Bank, (48) of Africa’s cities are growing by 10% a year, the swiftest (49) of urbanization ever recorded.
Is the trend good or bad Can the cities cope No one knows (50) . Without question, urbanization has produced (51) so ghastly that they are difficult to comprehend. In Cairo, children who (52) might be in kindergarten can be found digging through clots of ox waste, looking for (53) kernels of corn to eat. Young, homeless thieves in Papua New Guinea’s Port Moresby may not (54) their last names or the names of the villages where they were born. In the inner cities of America, newspapers regularly report on newborn babies (55) into garbage bins by drug-addicted mothers.