2014年6月托福考试模拟试题及答案(第一套)_第2页

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　　Scant physical evidence remains of the first human domestication of grain. Still, there is enough to conclude that ancient peoples, motivated by the nutritional value of bread or cakes made of wild wheat, looked for controlled ways to grow it to provide a consistent food supply. Three related discoveries are likely to have led to the introduction of bread as the first grain-based food.

　　The first discovery was that wheat could be prepared for use by grinding. People probably began consuming wheat by chewing it raw. Because wheat is very hard, they gradually discovered that it was less trouble to eat if crushed to paste between two stones—the result would have been the ancestor of the drier, more powdery wheat flour we use today.

　　From there, it was a short step to the next breakthrough: baking the simplest bread, which requires no technology but fire. Loaves of wheat paste, when baked into bread, could be stored for long periods, certainly longer than raw seeds. This kept the food value of wheat available for an extended period after it had been harvested.

　　Finally, ancient peoples found that, if the paste was allowed to sit in the open, yeast spores from the air settled on it and began fermenting the wheat. This natural process of fermentation caused bubbles to from in the wheat paste that suggested it would be lighter in texture and even easier to eat when baked.