来自《耶鲁大学开放课程：有关食物的心理学、生物学和政治学 第11集 第11集》

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  You can see the numbers yourselves, but at one point,
  你可以自己看看这些数字 但曾经
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  there were many, many varieties of foods in the environment.
  环境中有非常非常多种食物
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  People grow different strains of things right near each other,
  人们将不同品种的作物种在一起
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  and now that's really been reduced a lot.
  而如今 品种数大幅下降
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  Here is a map showing the crop distribution around the country,
  这张地图显示了全国的作物分布情况
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  and if you look at some of the Midwestern states,
  先看看中西部的一些州
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  the yellow segments there represent parts of states
  这里的黄色代表这些州有一部分
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  that are soybean and corn growers.
  种植了大豆和玉米
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  As you can see there is that big pocket through the Midwest
  你可以看到在中西部这块口袋型的区域
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  where basically those are the two only two things grown,
  基本就只有这两种作物
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  and then wheat would be true in other places like Kansas.
  而在其他地方 像堪萨斯州则只有小麦
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  Then as farmers shrink the number of varieties
  随着农民为迎合市场需求