单项选择题

Over half the world’s people now live in cities. The latest "Global Report on Human Settlements" says a significant change took place last year. The report 1 this week from U.N. Habitat, a United Nations agency.
A century ago, 2 than five percent of all people lived in cities. 3 the middle of this century it could be seventy percent, or 4 six and a half billion people.
Already three-fourths of people in 5 countries live in cities. Now most urban population 6 is in the developing world.
Urbanization can 7 to social and economic progress, but also put 8 on cities to provide housing and 9 . The new report says almost two hundred thousand people move 10 cities and towns each day. It says worsening inequalities, 11 by social divisions and differences in 12 , could result in violence and crime 13 cities plan better.
Another issue is urban sprawl (无序扩展的城区). This is where cities 14 quickly into rural areas, sometimes 15 a much faster rate than urban population growth.
Sprawl is 16 in the United States. Americans move a lot. In a recent study, Art Hall at the University of Kansas found that people are moving away from the 17 cities to smaller ones. He sees a 18 toward "de-urbanization" across the nation. 19 urban economies still provide many 20 that rural areas do not.

A.abilities
B.qualities
C.possibilities
D.realities