题目内容
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The shark's best sense is smell because ______.
A．most of its brain is used for this purpose
B．it is colour blind
C．it can smell blood from a quarter of a mile away
D．it can only see up to fifty feet
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Sewage and garbage attract sharks inland. When floods carry garbage to the rivers they provide a rich diet which sometimes stimulates an epidemic of shark attacks. Warm water generally provides shark food, and a rich diet inflames the shark's aggression.
In British waters sharks usually swim peacefully between ten and twenty miles offshore where warm water currents fatten mackerel and pilchards for their food. But the shark is terrifyingly unpredictable. One seaman was severely mauled as far north as Wick in Scotland. Small boats have been attacked in the English Channel, Irish Sea and North Sea.
Most of the legends about sharks are founded in ugly fact. Even a relatively small shark——a 200 lb. Zambezi——can sever a man's leg with one bite, Sharks have up to seven rows of teeth and as one front tooth is damaged or lost another moves forward to take its place. The shark never sleeps. Unlike most fish, it has no air bladder, and it must move constantly to avoid sinking. It is a primitive creature, unchanged for sixty million years of evolution. Its skin is without the specialized scales of a fish. Fully grown, it still has five pairs of separate gills like a three-week human embryo.
But it is a brilliantly efficient machine. Its skin carries nerve endings which can detect vibrations from fish moving several miles away. Its sense of smell, the function of most of its brain, can detect one part in 600,000 of tuna fish juice in water, or the blood of a fish or animal from a quarter of a mile away. It is colour blind, and sees best in deep water, but it can distinguish shapes and patterns of light and shade easily. Once vibrations and smell have placed its prey the shark sees well enough to home in by vision for the last fifty feet. The shark eats almost anything. It will gobble old tin cans and broken bottles as well as fish, animals and humans. Beer bottles, shoes, wrist watches, car number plates, overcoats and other sharks have been found in dead sharks. Medieval records tell of entire human corpses still encased in armour.
The United States military advice on repelling sharks is to stay clothed——sharks go for exposed flesh, especially the feet. Smooth swimming at the surface is essential. Frantic splashing will simply attract sharks, and dropping below the surface makes the swimmer an easy target.
If the shark gets close, then is the time to kick, thrash and hit out. A direct hit on the snout, gills, or eyes will drive away most sharks. The exception is the Great White shark. It simply kills you.
It is less common to find sharks in ______.
A．salt water
B．fresh water
C．warm water
D．deep water
It looked like a scene from Jaws but without the dramatic music. A huge shark was slowly swimming through the water, its tail swinging back and forth like the pendulum of a clock.
Suddenly sensitive nerve ending in the shark's skin picked up vibrations of a struggling fish. The shark was immediately transformed into a deadly, efficient machine of death. With muscles taut, the shark knifed through the water at a rapid speed. In a flash the shark caught its victim, a large fish, in its powerful jaws. Then, jerking its head back and forth, the shark tore huge chunks of flesh from its victim and swallowed them. Soon the action was over.
Moving to Survive
In pursuing its prey, the shark demonstrated in a dramatic way the important role of movement, or locomotion, in animals.
Like the shark. most animals use movement to find food. They also use locomotion to escape enemies, find a mate, and explore new territories. The methods of locomotion include crawling, hopping, slithering, flying, swimming, or walking.
Humans have the added advantage of using their various inventions to move about in just about any kind of environment. Automobiles, rockets, and submarines transport humans from deep oceans to as far away as the moon. However, for other animals movement came about naturally through millions of years of evolution. One of the most successfiil examples of animal locomotion is that of the shark. Its ability to quickly zero in on its prey has always impressed scientists. But it took a detailed study by Duke University marine biologists S. A. Wainwright, F. Vosburgh, and J. H. Hebrank to find out how the sharks did it. In their study the scientists observed sharks swimming in a tank at Marine land in Saint Augustine, Fla. Movies were taken of the sharks' movements and analyzed. Studies were also made of shark skin and muscle.
Skin Is the Key
The biologits discovered that the skin of the shark is the key to the animal's high efficiency in swimming through the water. The skin contains many fibers that cnsscross like the inside of a belted radial tire. The fibers are called collagen (胶原 ) fibers. These fibers can either store or release large amounts of energy depending on whether the fibers are relaxed or taut. When the fibers are stretched. energy is stored in them the way energy is stored in the string of a bow when pulled tight. When the energy is released, the fibers become relaxed.
The Duke University biologists have found that the greatest stretching occurs where the shark bends its body while swimming. During the body's back and forth motion, fibers along the outside part of the bending body stretch greatly. Much potential energy is stored in the fibers. This energy is released when the shark's body snaps back the other way.
As energy is altemately stored and released on both sides of the animal's body, the tail whips strongly back and forth. This whip-like action propels the animal through the water like a living bullet.
Source of Energy .
What causes the fibers to store so much energy？ In finding the answer the Duke University scientists leamed that the shark's similarity to a belted radial tire doesn't stop with the skin. Just as a radial tire is inflated by pressure, so, too, is the area just under the shark's collagen "radials". Instead of air pressure, however, the pressure in the shark may be due to the force of the blood pressing on the collagen fibers.
When the shark swims slowly, the pressure on the fibers is relatively low. The fibers are more relaxed, and the shark is able to bend its body at sharp angles. The animal swims this way when looking around for food orjust swimming However, when the shark detects an important food source, some fantastic involuntary changes take place.
The pressure inside the animal may increase by 10 times. This pressure change greatly stretches the fibers, enabling much energy to be stored.
This energy is then transferred to the tail, and the shark is off. The rest of the story is predictable.
Dolphin Has Speed Record
Another fast marine animal is the dolphin. This seagoing mammal has been clocked at speeds of 32 kilometers (20 miles) an hour. Biologists studying the dolphin have discovered that, like the shark, the animal's efficient locomotion can be traced to its skin. A dolphin's skin is made up in such a way that it offer very little resistance to the water flowing over it. Normally when a fish or other object moves slowly through the water, the water flows smoothly past the body. This smooth flow is known as laminarflow (层流 ). However, at faster speeds the water becomes more turbulent along the moving fish. This turbulence muses friction and slows the fish down.
In a dolphin the skin is so flexible that it bends and yields to the waviness of the water.
The waves, in effect, become tucked into the skin's folds. This allows the rest of the water to move smoothly by in a laminar flow. Where other animals would be slowed by turbulent water at rapid speeds, the dolphin can race through the water at record breaking speeds.
Other Animals Less Efficient
Not all animals move as efficiently as sharks and dolphins. Perhaps the greatest loser in locomotion efficiency is the slug (鼻涕虫). The slug, which looks like a snail without a shell, lays down a slimy trail over which it crawls. It uses so much energy producing the slimy mucus and crawling over it that a mouse traveling the same distance uses only one twelfth as much energy.
Scientists say that because of the slug's inefficient use of energy, its lifestyle. must be restricted. That is, the animals are forced to confine themselves to small areas for obtaining food and finding proper living conditions. Have humans ever been faced with this kind of problem？
1. According to the passage, a shark finds its prey by____.
A. smelling
B. the sense of hearing
C. feeling
D. the sense of sight
— Read the on the opposite page about an awards scheme for companies.
— Choose the best sentence from below to fill each of the gaps.
— For each gap 8 - 12, mark one letter (A - G) on your Answer Sheet.
— Do not use any letter more than once.
— There is an example at the beginning, (0).
The region's best smaller companies
Once again, readers of this magazine have the chance to vote for the region's best companies. (0)The awards will be presented at a dinner in Birmingham on May 17.
The pattern established in the first year, of awards for Best Established Company, Best New Company and Best Entrepreneur, will of course continue. However this year sees a new category, that of Best Communication with Investors. 【8】______
The Established Company of the Year will be one whose success has lasted for more than just a couple of months or years. Its share price will be performing above the average for its sector, but that is not the only measurement which will be taken into account. 【9】______ Above all, the winner will be professionally managed, in a way that deals equally well with good and bad trading conditions.
The New Company of the Year 'will have gone public last year, but will already have shown its growth and management qualities. 【10】______ In fact three early winners have already been successful in this second category, as well.
The Entrepreneur of the Year will be someone with a proven track record of expertise in setting up and providing leadership to one or possibly more businesses. He or she will have created an organisation that can deal with the demands placed on it as a public company. 【11】______ The winner will have maintained a balance between that original energy and the need to adapt as the company grows.
In our new category, Best Communication with Investors, the winning company will show that it is engaging in two-way dialogue with both actual and potential investors. 【12】______ All of these communication channels will be carefully tailored for the intended audience. In addition, the company is likely to distribute press releases by electronic means, to maximise its opportunities for publicity.
Nominations for awards were invited several months ago, and reduced by the judges to a shortlist of three in each category. The shortlisted companies are described below, together with details of how to vote. Please get your vote to us no later than 31 March.
A. It will, in effect, be able to demonstrate that it can go on to become an Established Company of the Year before long,
B. In order to win, the company will have achieved success in both spheres, and have the evidence to prove it.
C. To achieve this, it will be using a variety of means, including the annual report, presentations, a dedicated website and attendance at specialised exhibitions.
D. The judges will also consider the degree to which the company has a well planned and soundly financed strategy for its growth and development.
E. At the same time, this structure must not stifle the spirit that led to the company's initial SUCCESS.
F. The innovation has been made in order to recognise the increasingly important part which this factor plays in a company's success.
G. The competition, which is now in its tenth year, is designed to encourage excellence in smaller public companies based in this area.
There is widespread international support for ______.
A．Burma's opposition National League for Democracy and its leader Aung San Suu Kyi
B．Cambodian Prime Minister Hun Sen
C．Singapore Prime Minister Lee Hsien Loong
D．Burma's military
A.Tiger
B.Flying fish
C.Black Mamba
D.Shark
What is the key to the shark’s swift locomotion in water？
A．The skin.
B．The tail.
C．The muscle.
D．The jaw.
What is NOT mentioned as a reason for the market's popularity？
A．The range of food
B．The sense of community
C．The affordable prices
D．The quality of the produce
A. Ask yourself a question about the topic sentence.
B. Answer the question, and your answer(s) can be thesupporting point(s).
C. Develop those points in the sen tences.
D. All of the above
Different from most fishes, shark's body is not upheld by ______.
A．fiber
B．bones
C．cartilage
D．skeleton
A.repelled
B.retrieved
C.retained
D.restored
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