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39：Yeasts capable of leavening bread are widespread, and in the many centuries during which the ancient Egyptians made only unleavened bread, such yeasts must frequently have been mixed into bread doughs accidentally. The Egyptians, however, did not discover leavened bread until about 3000 B. C. That discovery roughly coincided with the introduction of a wheat variety that was preferable to previous varieties because its edible kernel could be removed from the husk without first toasting the grain.

Which of the following, if true, provides the strongest evidence that the two developments were causally related?

A.   Even after the ancient Egyptians discovered leavened bread and the techniques for reliably producing it were well known, unleavened bread continued to be widely consumed.

B.   Only when the Egyptians stopped the practice grain were their stone-lined grain-toasting pits available for baking bread.

C.   Heating a wheat kernel destroys its gluten, a protein that must be present in order for yeast to leaven bread dough.

D.   The new variety of wheat, which had a more delicate flavor because it was not toasted, was reserved for the consumption of high officials when it first began to be grown.

E.    Because the husk of the new variety of wheat was more easily removed, flour  Made from it required less effort to produce.

答案选C           请教NN们为什么呀？

Yeasts capable of leavening bread are widespread, and in the many centuries during which the ancient Egyptians made only unleavened bread, such yeasts must frequently have been mixed into bread doughs accidentally. The Egyptians, however, did not discover leavened bread until about 3000 B. C. That discovery roughly coincided with the introduction of a wheat variety that was preferable to previous varieties because its edible kernel could be removed from the husk without first toasting the grain.

Basic knowledge: edible kernel must be removed from the husk to produce dough the main ingredient of bread.

A wheat variety was preferable to the other, because the traditional toasting process is eliminated for producing dough

If this toasting process---the heat---destroys a necessary protein for leavening the bread, even yeasts frequently mixed into the bread, the chemical reaction would not occur.

Conclusion, it was not until the new wheat verity was introduced that the dough can be removed from its husk without heating (toasting), that the protein necessary for fermentation preserved from such process, and that the leavening process taken place, given that yeasts are frequently mix into the bread dough accidental. Consequently, yeasts are capable of leavening bread are discovered.