题目内容：
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 （S1） just around the next corner. The fast-growing population’s demand for food, they warned, would soon exceed their （S2） 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 （S3） spots like present-day Somalia, and occasional years of good harvests, the world’s food crisis has remained just （S4） around the corner. 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, economic and environmental reasons. Optimists （S6） point to concrete examples of continued improvements in yield. In Africa, by instance, improved seed, more （S7） fertilizer and advanced growing practices have more than double corn and wheat yields in an experiment. Elsewhere, （S8） rice experts in the Philippines are producing a plant with few （S9） stems and more seeds. There is no guarantee that plant breeders can continue to develop new, higher-yielding crop, but most researchers see their success to date as reason （S10） for hope.
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