听力原文：W: In Britain we are often told that people are leaving the big cities to live in the countryside but is this tile case worldwide? M: Not at all. If you look at the biggest cities in 1950, seven out of the top ten were in the developed countries. However, by the year 2000, the developing countries will have eight out of the top ten.New York, which in 1950 was number one with a population of around 12 million, will only be the sixth largest city in the world with an extra of 2 million. W: And London? M: London, which was number two, won't even be in the top ten. Its population in 1950 was about 10 million. W: Why is this happening? Why are people moving to tile big cities from the country in developing countries? M: The reasons are complex but many are moving to look for jobs. And the problems this creates are enormous. Just imagine the kinds of difficulties this is going to cause in terms of health, transport and education. W: Yes. What about the cities of Asia? Will they be experiencing a similar sort of growth? M: In some cases, yes. Calutta in India which was No. 10 in the league in 1950 is expected to be the fourth biggest city in the world with a population of 16 million, four times in its size in just 50 years. W: What about Japan? M: Ah! Well, Tokyo was number three in 1950 at the beginning of the next century, its population will increase by 18 million, three times of the year 1950.Looking at the other major cities in Asia, Shanghai and Seoul will be in the top ten as well but, perhaps surprisingly, not Beijing or Hong Kong. (23)