第三篇 Egypt Felled by Famine Even ancient Egypts mighty pyramid builders were powerless in the face of the famine that helped bring down their civilian 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 blem — and the same or worse could happen today. The ancient Egyptians depended on the Niles 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；使变小) 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 signature(名；特征) from that of the White Nile. So by analyzing isotope(同位素；核素) differences in mud deposited in the Nile Delta, Michael Krom of Leads 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 predates the fall of the Egypts 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. According to Krom, Egypts Old Kingdom fell

A. immediately after a period of drought.
B. immediately after a period of flood.
C. just before a drought struck.
D. just before a flood struck.