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9集 第9集》
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where you're not getting就是在增加了用水量之后 -
much additional return for much more water.所得到的收益不再和投入持平 -
These kind of calculations这一部分的考虑 -
have been long part of the farming system;也一直是农业系统中的一部分 -
people understand what they are人们理解这一点 -
and try to do the best to yield cost-benefit.并试图通过成本效益得到最大产量 -
It's very similar, for example,同样的 比如说 -
to calculations that people make about人们会计算让一头 -
how long do you allow a nursing cow to feed its calf?母牛喂养它的牛犊多久 -
Because the milk that the cow因为这头奶牛所产出的牛奶 -
is producing is valuable in the marketplace,同时也拥有一定的市场价值 -
but of course it's important但很显然