阅读理解：每篇文章后有5道题。要求应试者根据文章的内容，从每题所给的4个选项中选择1个最佳答案。
Ancient Egypt Brought Down by Famine
Even ancient Egypts mighty pyramidbuilders were powerless in the face of the faminethat helped bring down their civilization around 2180 B.C..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 Niles annual floods to irrigate their crops.But any change in climate that pushed the African monsoonssouthwards out of Ethiopia would have reduced these floods.
Declining rains in the Ethiopian highlands would have meant fewer plants to stabilize the soil.W.1len rain did fall it would have washed large amounts of soil into the Blue Nile and into Egypt，along with sedimentfrom the White Nile.
Blue Nile mud has a different isotopesignature from that of the white Nile.So by analyzing isotope differences in mud deposited in the Nile Delta.Michael Krom of LeedsUniversity 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 Egypts old Kingdom.
The weakened waters would have been disaster for the Egyptians.Changes that affect food supply dont have to be very large to have a rippleeffect 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.ascientist 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 today because the populations have increased dramatically.
1 Why does the author mention Egypts mighty pyramid builders?
A Because they once worked miracles.
B Because they were wellbuilt.
C Because they were actually very weak.
D Because even they were unable to rescue their civilization.
2 Which of the following factors was ultimately responsible for bringing down the civilization of ancient Egypt?
A Change of climate.
B Corrulption.
C flood.
D Population growth.
3 which of the following statements is true?
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 is a branch of the River Nile.
4 According to Krom，the Egypts o1d 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.
5 The word devastating in the last paragraph could be best replaced by
A frustrating.
B damaging.
C defeating.
D worrying.
KEY:DADAB