单项选择题

Take a look around on October 12, because it may seem a bit more crowded. On that day, or thereabouts, Earth’ s population will reach six billion. Although no one knows exactly when baby number six billion will arrive, the United Nations picked October 12 to mark the event, which is almost certain to occur before the end of 1999.
Six billion is a milestone (里程碑). The 20th century began with world population under two billion. We’ ye added the last billion people in only 12 years.
Most of the increase these days takes place in the developing world. Birthrates have remained at low levels in Europe and North A- merica. In the developing world the over all rate of increase is 1.7 percent a year, which would double its population in 40 years.

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