21、
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 2180BC. Now evidence gleaned 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 southwards out of Ethiopia would have diminished these floods.
Dwindling 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 from the White Nile.
The Blue Nile mud has a different isotope 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 predates the fall of the Egypts Old Kingdom.
The weakened waters would have been catastrophic for the Egyptians. Changes that affect food supply dont have to be very large to have a ripple 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 geoarchaeologist 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.
1. Why does the author mention pyramid builders?
A. because they once worked miracles.
B. because they were well-built
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 the fall of the civilization of ancient Egypt?
A. Change of climate
B. famine
C. food
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 Bile
C. The White Nile a branch of the Blue Nile
D. The White Nile and the Blue Nile are branches of the River Nile
4. 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
5. The word devastating in the last paragraph could be best replaced by
A. frustrating
B. damaging
C. defeating
D. worrying
标准答案： D,A,D,A,B
22、
spacing in animals
Flight Distance
Any observant person has noticed that a wild animal will allow a man or other potential enemy to approach only up to a given distance before it flees. “Flight distance” is the terms used for this interspecies spacing. As a general rule, there is a positive relationship between the size of an animal and its flight distance—the large the animal, the greater the distance it must keep between itself and the enemy. An antelope will flee when the enemy is as much as five hundred yards away. The wall lizard’s flight distance, on the other hand is about six feet. Flight is the basic means of survival for mobile creatures.
Critical Distance
Critical distance apparently is present wherever and whenever there is a flight reaction. Critical distance includes the narrow zone separating flight distance from attack distance. A lion in a zoo will flee from an approaching man until it meets a barrier that it cannot overcome. If the man continues the approach, he soon penetrates the lions critical distance, at which point the cornered lion reverses direction and begins slowly to stalk the man.
Social Distance
Social animals need to stay in touch with each other. Loss of contact with the group can be fatal for a variety of reasons including exposure to enemies. Social distance is not simply the distance at which an animal will lose contact with his group -- that is, the distance at which it can no longer see, hear, or smell the group -- it is rather a psychological distance, one at which the animal apparently begins to feel anxious when he exceeds its limits. We can think of it as a hidden band that contains the group.
Social distance varies from species to species. It is quite short -- apparently only a few yards -- among some animals, and quite long among others.
Social distance is not always rigidly fixed but is determined in part by the situation. When the young of apes and humans are mobile but not yet under control of the mothers voice, social distance may be the length of her reach. This is readily observed among the baboons(狒狒) in a zoo. When the baby approaches a certain point, the mother reaches out to seize the end of its tail and pull it back to her. When added control is needed because of danger, social distance shrinks. To show this in man, one has only to watch a family with a number of small children holding hands as they cross a busy street.
练习：
1. Which of the following is the most appropriate definition of Flight Distance?
A. Distance between animals of the same species before fleeing.
B. Distance between large and small animals before fleeing.
C. Distance between an animal and its enemy before fleeing.
D. Distance between certain animal species before fleeing.
2. If an animal’s critical distance is penetrated, it will
A. begin to attack.
B. try to hide.
C. begin to jump.
D. run away.
3. According to the passage, social distance refers to
A. physical distance.
B. psychological distance.
C. physiological distance.
D. philosophical distance.
4. Which of the following could best replace the word “band ” in “We can think of it as a hidden band that contains the group”(in Paragraph 3)?
A. strip of land.
B. distance.
C. society.
D. community.
5. The example of the children holding hands when crossing the street in the last paragraph shows that
A. social distance is not always needed.
B. there is no social distance among small children.
C. humans are different from animals in social distance.
D. social distance is sometimes determined by outside factors.
标准答案： C,A,B,A,D
23、
责任编辑：虫虫
