? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?{{B}}Spacing in Animals{{/B}} ? ?{{I}}Flight Distance{{/I}} ? ?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 larger 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. ? ?{{/I}}Critical Distance{{/I}} ? ?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 lion’s critical distance, at which point the cornered lion reverses direction and begins slowly to stalk the man. ? ?{{I}}Social Distance{{/I}} ? ?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 mother’s voice, social distance may be the length of her reach. This is readily observed among the baboons 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.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?{{B}}Spacing in Animals{{/B}} ? ?{{I}}Flight Distance{{/I}} ? ?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 larger 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. ? ?{{/I}}Critical Distance{{/I}} ? ?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 lion’s critical distance, at which point the cornered lion reverses direction and begins slowly to stalk the man. ? ?{{I}}Social Distance{{/I}} ? ?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 mother’s voice, social distance may be the length of her reach. This is readily observed among the baboons 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.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? {{B}}The World’s Longest Bridge{{/B}}
? ?Rumor has it that a legendary six-headed monster lurks in the deep waters of the Tyrrhenian Sea between Italy and the island of Sicily. {{U}}?(46) ?{{/U}}When completed in 2010, the world’s longest bridge will weigh nearly 300,000 tons — equivalent to the iceberg that sank the Titanic — and stretch 5 kilometers long. "That’s nearly 50 percent longer than any other bridge ever built," says structural engineer Shane Rixon.
? ?{{U}} ?(47) ?{{/U}}They’re suspension bridges, massive structures built to span vast water channels or gorges. A suspension bridge needs just two towers to shoulder the structure’s mammoth weight, thanks to hefty supporting cables slung between the towers and anchored firmly in deep pools of cement at each end of the bridge. The Messina Strait Bridge will have two 54,100-ton towers, which will support most of the bridge’s load. The beefy cables of the bridge, each 1.2 meter in diameter, will hold up the longest and widest bridge deck ever built.
? ?When construction begins on the Messina Strait Bridge in 2005, the first job will be to erect two 370 meter-tall steel towers. {{U}}?(48) ?{{/U}}Getting these cables up will be something. It’s not just their length — totally 5.3 kilometers — but their weight. {{U}}?(49) ?{{/U}}
? ?After lowering vertical "suspender" cables from the main cables, builders will erect a 60 meter-wide 54,630-ton steel roadway, or deck — wide enough to accommodate 12 lanes of traffic. The deck’s weight will pull down on the cables with a force of 70,500 tons. In return, the cables yank up against their firmly rooted anchors with a force of 139,000 tons — equivalent to the weight of about 100,000 cars. Those anchors are essential. {{U}}?(50) ?{{/U}}
? ?A ?Some environmentalists are against the project on biological grounds.
? ?B ?What do the world’s longest bridges have in common?
? ?C ?If true, one day you might spy the beast while zipping (呼啸而过) across the Messina Strait Bridge.
? ?D ?They’re what will keep the bridge from going anywhere.
? ?E ?The second job will be to pull two sets of steel cables across the strait, each set being a bundle of 44,352 individual steel wires.
? ?F ?They will tip up the scales at 166,500 tons — more than half the bridge’s total mass.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? {{B}}The World’s Longest Bridge{{/B}}
? ?Rumor has it that a legendary six-headed monster lurks in the deep waters of the Tyrrhenian Sea between Italy and the island of Sicily. {{U}}?(46) ?{{/U}}When completed in 2010, the world’s longest bridge will weigh nearly 300,000 tons — equivalent to the iceberg that sank the Titanic — and stretch 5 kilometers long. "That’s nearly 50 percent longer than any other bridge ever built," says structural engineer Shane Rixon.
? ?{{U}} ?(47) ?{{/U}}They’re suspension bridges, massive structures built to span vast water channels or gorges. A suspension bridge needs just two towers to shoulder the structure’s mammoth weight, thanks to hefty supporting cables slung between the towers and anchored firmly in deep pools of cement at each end of the bridge. The Messina Strait Bridge will have two 54,100-ton towers, which will support most of the bridge’s load. The beefy cables of the bridge, each 1.2 meter in diameter, will hold up the longest and widest bridge deck ever built.
? ?When construction begins on the Messina Strait Bridge in 2005, the first job will be to erect two 370 meter-tall steel towers. {{U}}?(48) ?{{/U}}Getting these cables up will be something. It’s not just their length — totally 5.3 kilometers — but their weight. {{U}}?(49) ?{{/U}}
? ?After lowering vertical "suspender" cables from the main cables, builders will erect a 60 meter-wide 54,630-ton steel roadway, or deck — wide enough to accommodate 12 lanes of traffic. The deck’s weight will pull down on the cables with a force of 70,500 tons. In return, the cables yank up against their firmly rooted anchors with a force of 139,000 tons — equivalent to the weight of about 100,000 cars. Those anchors are essential. {{U}}?(50) ?{{/U}}
? ?A ?Some environmentalists are against the project on biological grounds.
? ?B ?What do the world’s longest bridges have in common?
? ?C ?If true, one day you might spy the beast while zipping (呼啸而过) across the Messina Strait Bridge.
? ?D ?They’re what will keep the bridge from going anywhere.
? ?E ?The second job will be to pull two sets of steel cables across the strait, each set being a bundle of 44,352 individual steel wires.
? ?F ?They will tip up the scales at 166,500 tons — more than half the bridge’s total mass.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? {{B}}Water{{/B}} ? ?From the beginning, water has furnished man with a source of food and a highway to travel upon. The first civilizations arose{{U}} ?(51) ?{{/U}}water was a dominant element in the environment, a challenge{{U}} ?(52) ?{{/U}}man’s ingenuity. The Egyptians invented the 365-day calendar in response to the Nile’s annual flooding. The Babylonians, {{U}}?(53) ?{{/U}}were among the most famous law-makers in ancient times, invented laws{{U}} ?(54) ?{{/U}}water usage. Water inspired the Chinese to build a 1,000-{{U}} ?(55) ?{{/U}}canal, a complex system which, after nearly 2,500 years, remains still practically{{U}} ?(56) ?{{/U}}and still commands the astonishment of engineers. But{{U}} ?(57) ?{{/U}}never found complete solutions to their water problems. The Yellow River is also known as "China’s Sorrow"; it is so unpredictable and dangerous{{U}} ?(58) ?{{/U}}in a single flood it has caused a million{{U}} ?(59) ?{{/U}}. Floods slowed the great{{U}} ?(60) ?{{/U}}of the Indus River Valley, and inadequate drainage ruined{{U}} ?(61) ?{{/U}}of its land. Today water dominates man{{U}} ?(62) ?{{/U}}it always has done. Its presence continues to{{U}} ?(63) ?{{/U}}the location of his homes and cities; its violent variability can{{U}} ?(64) ?{{/U}}man or his herds or his crops; its routes links him{{U}} ?(65) ?{{/U}}his fellows; its immense value may add to already dangerous political conflicts. There are many examples of this in our own time.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? {{B}}Water{{/B}} ? ?From the beginning, water has furnished man with a source of food and a highway to travel upon. The first civilizations arose{{U}} ?(51) ?{{/U}}water was a dominant element in the environment, a challenge{{U}} ?(52) ?{{/U}}man’s ingenuity. The Egyptians invented the 365-day calendar in response to the Nile’s annual flooding. The Babylonians, {{U}}?(53) ?{{/U}}were among the most famous law-makers in ancient times, invented laws{{U}} ?(54) ?{{/U}}water usage. Water inspired the Chinese to build a 1,000-{{U}} ?(55) ?{{/U}}canal, a complex system which, after nearly 2,500 years, remains still practically{{U}} ?(56) ?{{/U}}and still commands the astonishment of engineers. But{{U}} ?(57) ?{{/U}}never found complete solutions to their water problems. The Yellow River is also known as "China’s Sorrow"; it is so unpredictable and dangerous{{U}} ?(58) ?{{/U}}in a single flood it has caused a million{{U}} ?(59) ?{{/U}}. Floods slowed the great{{U}} ?(60) ?{{/U}}of the Indus River Valley, and inadequate drainage ruined{{U}} ?(61) ?{{/U}}of its land. Today water dominates man{{U}} ?(62) ?{{/U}}it always has done. Its presence continues to{{U}} ?(63) ?{{/U}}the location of his homes and cities; its violent variability can{{U}} ?(64) ?{{/U}}man or his herds or his crops; its routes links him{{U}} ?(65) ?{{/U}}his fellows; its immense value may add to already dangerous political conflicts. There are many examples of this in our own time.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? {{B}}Water{{/B}} ? ?From the beginning, water has furnished man with a source of food and a highway to travel upon. The first civilizations arose{{U}} ?(51) ?{{/U}}water was a dominant element in the environment, a challenge{{U}} ?(52) ?{{/U}}man’s ingenuity. The Egyptians invented the 365-day calendar in response to the Nile’s annual flooding. The Babylonians, {{U}}?(53) ?{{/U}}were among the most famous law-makers in ancient times, invented laws{{U}} ?(54) ?{{/U}}water usage. Water inspired the Chinese to build a 1,000-{{U}} ?(55) ?{{/U}}canal, a complex system which, after nearly 2,500 years, remains still practically{{U}} ?(56) ?{{/U}}and still commands the astonishment of engineers. But{{U}} ?(57) ?{{/U}}never found complete solutions to their water problems. The Yellow River is also known as "China’s Sorrow"; it is so unpredictable and dangerous{{U}} ?(58) ?{{/U}}in a single flood it has caused a million{{U}} ?(59) ?{{/U}}. Floods slowed the great{{U}} ?(60) ?{{/U}}of the Indus River Valley, and inadequate drainage ruined{{U}} ?(61) ?{{/U}}of its land. Today water dominates man{{U}} ?(62) ?{{/U}}it always has done. Its presence continues to{{U}} ?(63) ?{{/U}}the location of his homes and cities; its violent variability can{{U}} ?(64) ?{{/U}}man or his herds or his crops; its routes links him{{U}} ?(65) ?{{/U}}his fellows; its immense value may add to already dangerous political conflicts. There are many examples of this in our own time.