第十五期 7-1 (7/7)

50 years ago, most people lived in rural areas.

But the world has changed. By some point next year,

more than half of all people will live in cities,

for the first time in history.

So says the most recent estimate from the United Nations.

City life is not always a bad thing,

but many experts worry about this process of urbanization.

A new report says it is having a huge effect on human health

and the quality of the environment.

Of the 3 billion people who live in cities now,

the report says, about 1 billion live in unplanned settlements.