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  3. Thomas Malthus published his "Essay on the Principle of Population" almost 200 years ago. Ever since then, forecasters have bein

Thomas Malthus published his "Essay on the Principle of Population" almost 200 years ago. Ever since then, forecasters have bein

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问题     Thomas Malthus published his "Essay on the Principle of
Population" almost 200 years ago. Ever since then, forecasters have
being warning that worldwide famine was just around the next comer.             【S1】______
The fast growing population’s demand for food, they warned, would
soon exceed their supply, leading to the wide spread food shortages             【S2】______
and starvation.
    But in reality, the world’s total grain harvest has risen steadily over
the years. Except for relative isolated trouble spots like present-day          【S3】______
Somalia, and occasional years of good harvests, the world’s food crisis         【S4】______
has remained just around the comer. Most experts believe this can
continue even as if the population doubles by the mid-21st century,             【S5】______
although feeding 10 billion people will not be easy for politics,               【S6】______
economic and environmental reasons. Optimists point to concrete
examples of continued improvements in yield. In Africa, by instance,            【S7】______
improved seed, more fertilizer and advanced growing practices have
more than double com and wheat yield in an experiment. Elsewhere,               【S8】______
rice experts in the Philippines are producing a plant with few stems and        【S9】______
more seeds. There is no guarantee that plant breed can continue to              【S10】______
develop new, high-yielding crop, but most researchers see their success
to date as the reason for hope.
【S8】
选项
答案double→doubled
解析 时态错误。此处考查的是现在完成时的用法，所以要把have double改为have doubled。
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