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  3. Thomas Malthus published his Essay on the Principle of Populationalmost 200 yea

Thomas Malthus published his Essay on the Principle of Populationalmost 200 yea

游客2023-10-14  9
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 poor harvests, the world’s food crisis has remained【M4】_________
just around the comer.Most experts believe this can continue even as if【M5】_________
the population doubles by the mid-21st century, although feeding 10 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. [br] 【M7】
选项
答案 by→for
解析 该句的意思是“例如，在非洲，在一项试验中，改良种子、更多化肥和先进的种植方法使玉米和小麦产量增加了一倍以上”。for instance为固定用法，表示“例如”。因此将by改为for。
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