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 of toasting 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.
Which of the following most logically completes the passage?
A certain tropical island received food donations in the form of powdered milk for distribution to its poorest residents,who were thought to be malnourished.Subsequently,the rate of liver cancers among those islanders increased sharply.The donated milk was probably to blame:recent laboratory research on rats has shown that rats briefly exposed to the substance aflatoxin tend to develop liver cancer when fed casein,a milk protein.This result is relevant because ________.
A.in the tropics,peanuts,a staple of these island residents,support a mold growth that produces aflatoxin
B.the liver is more sensitive to carcinogens,of which aflatoxin may be one,than most other bodily organs
C.casein is not the only protein contained in milk
D.powdered milk is the most appropriate form in which to send milk to a tropical destination
E.the people who were given the donated milk had been screened for their ability to digest milk