Recently protein feeds for animals have been developed by growing yeast in a petroleumbased stock.
最近已经研制出一种动物食用的蛋白质饲料，它是用石油作为基本原料加上酵母而制成的。
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Diesel will cost more, but petroleum-based diesel sells in America for 57 cents a litre before distribution costs and tax, so there should be room for profit.