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

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

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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          【M1】 ______
that worldwide famine was just around the next comer. The fast-growing
population’s demand for food, they warned, would soon exceed their             【M2】 ______
supply, leading to widespread food shortages 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 Somalia,    【M3】 ______
and occasional years of good harvests, the world’s food crisis has remained    【M4】 ______
just around the comer. Most experts believe this can continue even as ff       【M5】 ______
the population doubles by the mid-21st century, although feeding l0 billion
people will not be easy for politics, economic and environmental reasons.      【M6】 ______
Optimists point to concrete examples of continued improvements in yield.
In Africa, by instance, improved seeds, more fertilizers and advanced          【M7】 ______
growing practices have more than double com and wheat yields in an             【M8】 ______
experiment. Elsewhere, rice experts in the Philippines are producing
a plant with few stems and more seeds. There is no guarantee that plant        【M9】 ______
breeders can continue to develop new, higher-yielding crop, but most           【M10】______
researchers see their success to date as reason for hope.
【M1】
选项
答案将being改为been。
解析 “have been+现在分词”为现在完成进行时，例如：I have been puzzling my brains about this question for weeks now．对这个问题我已经苦苦思索了几个星期。As we have been practicing regularly，we are certain of winning the game this time．我们一直在练习，这次有把握一定能取胜。
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