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.
相关推荐：
文都：2008年12月英语四级全真预测试卷(一) 2008年12月英语四级考试最后冲刺模拟试题 【打包下载】1989－2008年6月英语四级真题下载
