Source of Energy
What causes the fibers to store so much energy? In finding the answer the Duke University scientists learned that the sharks similarity to a belted radial tire doesnt stop with the skin. Just as a radial tire is inflated by pressure, so, too, is the area just under the sharks 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 or just 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 animals efficient locomotion can be traced to its skin. A dolphins skin is made up in such a way that it offers 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 laminar flow. 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 skins 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. 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 slugs 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.Automobiles, rockets, and submarines are all examples given to support the idea that human inventions enable us to travel in almost any kind of environment.
2.The tail of the shark contributes to its swift locomotion.
3.The greatest stretching of the collagen fibers occurs when a shark tears huge chunks of flesh from its prey.
4.The area just under the sharks collagen fibers is similar to a belted radial tire because it is also inflated by pressure.
5.A laminar flow is formed when a fish swims against the current.
6.Consuming the equal amount of energy as a slug does, a mouse can travel 12 times as long as a slug.
7.Most species of sharks, including very small ones, can endanger mans life.
1.[Y][N][NG]2.[Y][N][NG]3.[Y][N][NG]
4.[Y][N][NG]5.[Y][N][NG]6.[Y][N][NG]
7.[Y][N][NG]
8.A shark finds its prey by.
9.According to the passage, can be compared to the string of a bow for both of them store energy when stretched.
10.When the shark detects an important food source, take place.
Part IIIListening Comprehension (35 minutes)
Section A
Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and the questions will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked [A], [B], [C] and [D], and decide which is the best answer. Then mark the corresponding letter on Answer Sheet 2 with a single line through the centre.
11.[A] He had finished his work.
[B] He came to surprise his wife.
[C] He came for lunch.
[D] He came to fetch some document.
12.[A] At a library.
[B] In a bus.
[C] At the airport.
[D] At a post office.
13.[A] Theres a paper by the door.
[B] The paper must have blown away.
[C] He should look further under the desk.
[D] He can buy another one at the corner.
14. [A] 11: 25
[B] 11: 40
[C] 11: 46
[D] 11: 26
15.[A] The rent is too high.
[B] He cant afford the high taxes.
[C] He doesnt want to live in the suburbs.
[D] Its too far away from his office.
16.[A] No. He has to finish his homework.
[B] No. He doesnt like going to the club.
[C] Yes. Hell go after he finished his homework.
[D] Yes. Hell write his paper after he returns.
17. [A] She lost her way.
[B] She lost her keys.
[C] She lost her car.
[D] She lost her handbag.
18.[A] Worried and frightened.
[B] Very relaxed.
[C] Quite unhappy.
[D] Angry with the professor.
Questions 19 to 22 are based on the conversation you have just heard.
19. [A] In a classroom.
[B] In a snack bar.
[C] In the dormitory.
[D] In a camera shop.
20.[A] The mans brother.
[B] The mans roommate.
[C] A neighbor.
[D] A photographer.
21.[A] Hes noisy.
[B] Hes messy.
[C] He doesnt tell the truth.
[D] He doesnt close the door.
22.[A] He worked for a radio station.
[B] He lived in a dormitory.
[C] He took a long trip.
[D] He visited the mans family.
Questions 23 to 25 are based on the conversation you have just heard.
23.[A] One of his classes finished early.
[B] He wanted to get some studying done.
[C] The library had a special display on the Industrial Revolution.
[D] His books were ten days overdue.
24. [A] Checked them out.
[B] Took notes on them.
[C] Returned them to the shelves.
[D] Put them in his book bag.
25. [A] They are marked with colored labels.
[B] They are specially coded.
[C] They are checked out.
[D] They are inspected by the guard.本新闻共 6页,当前在第 2页 1 2 3 4 5 6 |
