[单项选择]At no time in history has there been such a mass movement of people from countryside to city 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 Many world’ s major cities are already struggling with out-of-date transport infrastructures.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 21^stcentury
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 But its transport systems are now hopelessly out-of-date, a
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