At no time in history has there been such a mass movement of people from countryside to ci

ty as is happening now. By the year 2030, it' s estimated that more than two thirds of the word' s population will be living in cities, twice as many as today. This means that the problems faced by cities to day-overcrowding, poor housing, unemployment, poverty, and lack of food water--will be twice as had in the next century, unless we find solutions soon.

Another serious issue is how to provide good transport to their citizens. Many world' s major cities are already struggling with out-of-date transport infrastructures. How can they deal with the additional demands in the 21stcentury？

London is a good example. It was the world' s first big city--the first with a population of a mil lion people. Its enlargement was made possible by the invention of the steam engine, which powered the world's first underground railway. But its transport systems are now hopelessly out-of-date, and need urgent modernization. London' s future success depends very much on transport.

Over a million people travel into central London every day from outside the city. They, and the people who live in London, want a public transport system that is fragment, safe and environmentally friendly. What they often get, however, falls far short of that ideal. Commuters complain about disorder, cost and pollution, while businesses worry about the problems their staff have in getting to work on time. Yet, the proportion of London households that own a car grew from just over 10 per cent in the early 1950s to over 60 percent today.

As the city has become increasingly crowded and polluted, there has been a growing realization that action is needed.

It is believed that ______.

A．overpopulation causes the problems in cities

B．two-thirds of the world' s population are living in cities today

C．it isn' t difficult to solve the problems faced by cities today

D．with fewer people, we would be free from any problems