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  3. Egypt Felled by Famine Even ancient Egypt’ s mighty pyramid builders were powerless in the face of the famine that helped br

Egypt Felled by Famine Even ancient Egypt’ s mighty pyramid builders were powerless in the face of the famine that helped br

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问题                         Egypt Felled by Famine
    Even ancient Egypt’ s mighty pyramid builders were powerless in the face of the famine that helped bring down their civilization around 2180 BC. Now evidence gleaned(搜集)from mud deposited by the River Nile suggests that a shift in climate thousands of kilometers to the south was ultimately to blame—and the same or worse could happen today.
    The ancient Egyptians depended on the Nile’ s annual floods to irrigate their crops. But any change in climate that pushed the African monsoons(季风)southwards out of Ethiopia would have diminished these floods.
    Dwindling(逐渐变少；使变少) rains in the Ethiopian highlands would have meant fewer plants to establish the soil. When rain did fall it would have washed large amounts of soil into the Blue Nile and into Egypt, along with sediment(沉积;沉积物)from the White Nile.
    The Blue Nile mud has a different isotope(同位素；核素)signature from that of the White Nile. So by analyzing isotope differences in mud deposited in the Nile Delta, Michael Krom of Leeds University worked out what proportion of sediment came from each branch of the river.
    Krom reasons that during periods of drought, the amount of the Blue Nile mud in the river would be relatively high. He found that one of these periods, from 4, 500 to 4, 200 years ago, immediately predated the fall of the Egypt’ s old Kingdom.
    The weakened waters would have been catastrophic for the Egyptians. "Changes that affect food supply don’ t have to be very large to have a ripple effect in societies, " says Bill Ryan of the Lamont Doherty Earth Observatory(天文台)in New York.
    " Similar events today could be even more devastating, " says team member Daniel Stanley, a geoarchaeologist(地质考古学家)from the Smithsonian Institution in Washington, D. C. "Anything humans do to shift the climate belts would have an even worse effect along the Nile system because the populations have increased dramatically. "
Which of the following statements is true?
选项 A、The White Nile is the trunk of the River Nile.
B、The White Nile is the trunk of the Blue Nile.
C、The White Nile is a branch of the Blue Nile.
D、The White Nile and the Blue Nile are branches of the River Nile.
答案D
解析 第四段指出：青尼罗河的泥浆与白尼罗河的泥浆的同位素标记不同。通过分析尼罗河三角洲的泥浆的同位素差别，利兹大学的迈克尔·克罗姆算出了来自每个支流的沉淀物的比例，由此可推断出青尼罗河和白尼罗河是尼罗河的支流，故选D。
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