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  3. 　　You can find a table below showing the population change from 2010 to 2030, projected by the Population Council in New York, a

　　You can find a table below showing the population change from 2010 to 2030, projected by the Population Council in New York, a

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问题 　　You can find a table below showing the population change from 2010 to 2030, projected by the Population Council in New York, and a short material explaining some conditions of population prediction. Read them carefully and write an essay of no less than 300 words, in which you should:
　　1.   summarize the ideas in both materials, and then
　　2.   comment on the situation.
选项
答案　　 Assumptions Underlying the Projections 　　The population of the world now increases every year because the global birth rate exceeds the death rate. The annual birth and death rates of populations are in turn primarily determined by levels of fertility and mortality experienced by individuals. The most widely used fertility indicator is the total fertility rate (TFR). Mortality is usually measured by the life expectancy at birth (LE), which equals the average number of years a newborn would live if subjected to a given set of age-specific mortality rates. In order to make long-range population projections, assumptions have to be made about the future trajectories of fertility and mortality. 　　Future trends in fertility in the South are based on the assumption that the total fertility rate will eventually reach and then remain at the so-called "replacement" level in all regions. Replacement fertility is just above 2 bpw and it represents the level at which each generation just replaces the previous one, thus leading to zero population growth. Below-replacement fertility produces, in the long run, population decline. 　　Mortality levels have also changed rapidly over the past few decades. By the early 1990s, Latin America had reached mortality levels similar to those prevailing in the North in the 1950s, and Asia was not far behind. Africa has had the highest mortality levels and the slowest rate of improvement. By 2025, mortality conditions in Asia and Latin America are expected to be similar to those that prevailed in the North in the 1970s. Africa will continue to lag, in part because the continent is most heavily affected by the AIDS epidemic. 　　It should be noted that the assumptions made by the UN about future trends in fertility and mortality are not based on a firm theoretical basis. Instead, the UN relies on empirical regularities in past trends in the now-developed countries, mostly in the North, where fertility declined to around the replacement level, and increases in life expectancy became smaller over time. This is a plausible approach that unfortunately leaves room for potential inaccuracies in projection results.
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