填空题
The year 2005is the midpoint of a decade that spans three
unique，important transition in the history of humankind.【S1】______
Before 2000，young people always outnumber old people.【S2】______
From 2000forward，old people will outnumber young
people.Until approximately 2007，rural people will have
always been outnumbered urban people.From approximately 【S3】______
2007forward，urban people will not outnumber rural people.
From 2003on，the median woman worldwide have had，and
will continue to have，too few or just enough children
during her lifetime to replace themselves and the father in 【S4】______
the following generation.
The century with 2000as its midpoint marks three
additional unique，important transitions in human history.
First，any person who died before 1930had lived through 【S5】______
a doubling of the human population.Nor is any person
born in 2050or later likely to live through a doubling of
the human population.On contrast，everyone 45years old 【S6】______
or elder today has seen more than a doubling of human 【S7】______
numbers from three billion in 1960to 6.5billion in 2005.
The peak population growth rate ever reached about 2.1
percent a year，that occurred between 1965and 1970.Human 【S8】______
population never grew with such the speed before the 20th 【S9】______
century and is never again likely to grow with such speed.
Our descendants will look back on the late 1960s peak like 【S10】______
the most significant demographic event in the history of
the human population even though those of us who lived
through it did not recognize it.