This pattern is important to notice. Not only does it put the current problems of demographic growth into a historical perspective, but it suggests that the cause of rapid increase in population in recent years is not a sudden enthusiasm for more children, but an improvement in the conditions that traditionally have caused high mortality.

　　Demographic history can be divided into two major periods: a time of long, slow growth which extended from about 8000 B．C. till approximately 1650 A．D.. In the first period of some 9,600 years, the population increased from some 8 million to 500 million in 1650. Between 1650 and 1975, the population has increased from 500 million to more than 4 billion. And the population reached 6.2 billion throughout the world by the year 2000.One way to appreciate this dramatic difference in such abstract numbers is to reduce the time frame to something that is more manageable. Between 8000 B．C. and 1650, an average of only 50,000 persons was being added annually to the world's population. At present， this number is added every six hours. The increase is about 800,000,000 persons annually.

　　本文讲述的是人口增长的历史，从公元前8000年到当前人口的增长情况进行分析。

　　5．The underlined word “demographic” in Paragraph 1 means ________.

　　A．extinction of human

　　B．statistics of human population

　　C．death rate of human

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