The world's exploding population signals even more growing pains ahead for already crowded

areas. A new United Nations study forecasts that by the year 2000,2 billion persons will be added to the 4.4 billion in the world today.

Even more troubling than the increasing number of inhabitants are the projections of where they will be concentrated. The study by Rafael M. Solos, executive director of the U. N. Fund for Population Activities, notes that by the year 2000:

Nearly 80 percent of all people will live in less developed countries, many hard pressed to support their present populations. That compares with 70 percent today.

In many of these Third World lands metropolises (大城市) will become centers of concentrated urban poverty because of a flood of migration from rural areas.

The bulging(膨胀的) centers mainly in Asia and Latin America, will increasingly become fertile fields for social unrest. More young residents of the urban clusters(一群) will be better educated, unemployed and demanding of a better lifestyle.

To slow the rush to urban centers, countries will have to vastly expand opportunities in the country side, the study suggests. Solos says: "The solution to the urban problem lies as much in the rural areas as in the cities themselves."

Worldwide, the numer of large cities ,will multiply. Now 26 cities have 5 million or more residents each and a combined population of 252 million. By the end of the decade, the number will escalate to 60. with an estimated total of almost 650 million people.

In the last paragraph, the word "escalate" means ______.

A．decrease

B．increase

C．go down

D．decline