【单选题】

The earth is witnessing an urban revolution, as people worldwide crowd into towns and cities. In 1800 only five per cent of the world’s population were urban dwellers; now the proportion has risen to more than forty-five percent, and by the year 2010 more people will live in towns and cities than in the countryside. Humanity will, for the first time, have become a predominantly urban species.

Though the world is getting more crowded by the day, absolute numbers of population are less important than where people concentrate and whether these areas can cope with them.Even densities, however, tell us nothing about the quality of the infrastructure—roads, housing and job creation, for example—or the availability of crucial services.
The main question, then, is not how many people there are in a given area, but how well their needs can be met.Density figures have to be set beside measurements of wealth and employment, the quality of housing and the availability of education, medical care, clean water, sanitation and other vital services. The urban revolution is taking place mainly in the Third World, where it is hardest to accommodate.
Between 1950 and 1985 the number of city dwellers grew more than twice as fast in the Third World as in industrialized countries.During this period, the urban population of the developed world increased from 477 million to 838 million, less than double; but it quadrupled in developing countries, from 286 million to 1.14 billion.Africa’s urban population is racing along at five percent a year on average, doubling city numbers every fourteen years.By the turn of the century, three in every four LatinAmericans will live in urban areas, as will two in every fiveAsians and one in every threeAfricans.Developing countries will have to increase their urban facilities by two thirds by then, if they are to maintain even their present inadequate levels of services and housing.
In 1940 only one out of every hundred of the world’s people lived in a really big city, one with a population of over a million.By 1980 this proportion had already risen to one in ten. Two of the world’s biggest cities, Mexico and Sao Paulo, are already bursting at the seams—and their populations are doubling in less than twenty years.
About a third of the people of the Third World’s cities now live in desperately overcrowded slums and squatter settlements. Many are unemployed, uneducated, undernourished and chronically sick. Tens of millions of new people arrive every year, flocking in from the countryside in what is the greatest mass migration in history.
Pushed out of the countryside by rural poverty and drawn to the cities in the hope of a better life, they find no houses waiting for them, no water supplies, no sewerage, no schools. They throw up makeshift hovels, built of whatever they can finD、sticks, fronds, cardboard, tar-paper, straw, petrol tins and, if they are lucky, corrugated iron. They have to take the land none else wants; land that is too wet, too dry, too steep or too polluted for normal habitation.
Yet all over the world the inhabitants of these apparently hopeless slums show extraordinary enterprise in improving their lives. While many settlements remain stuck in apathy, many others are gradually improved through the vigour and co-operation of their people, who turn flimsy shacks into solid buildings, build school, lay out streets and put in electricity and water supplies.
Governments can help by giving the squatters the right to the land that they have usually occupied illegally, giving them the incentive to improve their homes and neighborhoods. The most important way to ameliorate the effects of the Third World’s exploding cities, however, is to slow down the migration. This involves correcting the bias most governments show towards cities and towns and against the countryside. With few sources of hard currency, though, many governments in developing