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A．catch B．hold C．run into D．bump into
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Ancient Egypt Brought Down by Famine
Even ancient Egypt's mighty pyramid （金字塔） builders were powerless in the face of the famine （饥荒） that helped bring down their civilization around 21-80 BC． Now evidence collected 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 !heir crops.But any change in climate that pushed the African monsoons （季风） southwards out of Ethiopia would have reduced these floods.
Declining rains in the Ethiopian highlands would have meant fewer plants to stabilize 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） from the White Nile.Blue Nile mud has a different isotope （同位素） 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 Blue Nile mud in the river would be relatively high. He found that one of these periods, from 4500 to 4200 years ago, immediately came before the fall of the Egypt's Old Kingdom.
The weakened waters would have been disaster for the Egyptians. "Changes that affect food supply don't have to be very large to have a ripple （波浪） effect in societies," says Bill Ryan of the Lamont Doherty Earth Observatory in New York.
Similar events today could be even more devastating, says team member Daniel Stanley, a scientist from the Smithsonian Institution in Washington DC． "Anything humans do to shift the climate belts would have an even worse effect along the Nile system today because the populations have increased dramatically."
第 36 题 Why does the author mention "Egypt's mighty pyramid builders".
A．also B．besides C．alse D．yet
"Salty" Rice Plant Boosts Harvests
British scientists are breeding a new generation of rice plants that will be able to grow in soil containing salt water. Their work may enable abandoned farms to become productive once more.
Tim Flowers and Tony Yeo, from Sussex University's School of Biological Sciences,have spent several years researching how crops, such as rice, could be made to grow in,water that has become salty.
The pair have recently begun a three-year programme, funded by the Biotechnology and Biological sciences Research Council, to establish which genes enable some plants to survive salty conditions. The aim is to breed this capability into crops, starting with rice.
It is estimated that each year more than 10m hectares （公顷） of agricultural land are lost because salt gets into the soil and stunts （妨碍生长） plants. The problem is caused
by several factors. In the tropics, mangroves （红树林） that create swamps （沼泽） and traditionally formed barriers to sea water have been cut down. In the Mediterranean, a series of droughts have caused the water table to drop, allowing sea water to seep （渗透） in. In Latin America, irrigation often causes problems when water is evaporated （蒸发） by the neat, leaving salt deposits behind.
Excess salt then enters the plants and prevents them functioning normally. Heavy concentrations of minerals in the plants stop them drawing up .the water they need to survive.
To overcome these problems, Flowers and Yeo decided to breed rice plants that take in very little salt and store what they do absorb in cells that do not affect the plants'
,growth. They have started to breed these characteristics into a new rice crop, but it will take about eight harvests before the resulting seeds are ready to be considered for commercial use.
Once the characteristics for surviving salty soil are known, Flowers and Yeo will try to breed the appropriate genes into all manners of crops and plants. Land that has been abandoned to nature will then be able to bloom again, providing much needed food in the poorer countries of the world.
第 31 题 Which of the following statements about Flowers and Yeo is true.
What was scientists’ understanding of cryptic species？
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