老托30篇听力稿.docx

NO1:This morning I want to tell you about a recent scientific discovery dealing with the relationship between plants and animals. This is about a desert shrub whose leaves can shoot a stream of poisonous resin a distance of six feet. You think it would be safe from all attacks by insects? But a recent study has found one insect, a beetle that can chew its way past the plants defense system by cutting the main vein that delivers the poison to the leaves. This vein cutting is just one method the beetles used to prepare a safe meal. Another is by cutting a path all the way across the leaves to hold the flow of chemicals. Then they simply eat between the veins of poison. In the past, scientists who studied insect adaptation to plant defenses have focused on chemical responses. That is, how the insects can neutralize or alter the poisonous substances plants produce. Whats unique about this chewing strategy is that the beetle is actually exhibiting a behavioral response to the plants defenses rather than the more common chemical response. It is only after a beetles survived several encounters with the plants resin that it learns how to avoid the poison: by chewing through the resin transporting veins on the next leaf it eats. And thus gives itself a safe meal. However, it can take a beetle an hour and a half of careful vein cutting to prepare a small leaf that takes it only a few minutes to eat. So, though the method is effective, its not very efficient.NO2:Human populations near the equator have evolved dark skin over many generations because of exposure to the fiercest rays of the sun. A similar phenomenon has also occurred in other parts of the animal kingdom. The African grass mouse is a good example. Most mice are nocturnal, but the African grass mouse is active during daylight hours. This means that it spends its days searching for food in the semi-dry bush in scrubby habitats of eastern and southern Africa. Its furry stripes like a chipmunks, which helps it blend in with its environment. Because it spends a lot of time in the intense tropical sun, the grass mouse has also evolved two separate safeguards against the suns ultraviolet radiation. First, like the population of humans in this region of the world, the skin of the grass mouse contains lots of melanin, or dark pigment. Second and quite unusual, this mouse has a layer of melanin-pigmented tissue between its skull and skin. This unique cap provides an extra measure of protection for the grass mouse and three other types of African mouse, like rodents that are active during the day. The only other species scientists has identified with the same sort of skull adaptation is the white tent-making bat of the Central American tropics. Although these bats sleep during the day, they do so curled up with their heads exposed to the sun.NO3:Weve been looking at fear from a biological perspective, and someone asked whether the tendency to be fearful is genetic. What some studies done with mice indicate that mammals do inherit fearfulness to some degree. In one study, for instance, a group of mice was placed in a brightly lit open box with no hiding place. Some of the mice wandered around the box and didnt appear to be bothered about being so exposed. But other mice didnt move. They stayed up against one wall which indicated that they were afraid. Well, when fearful mice, or you might say anxious mice like the ones who stayed in one place, when mice like these were bred with one another repeatedly, after about twelve or so generations, then all of the offspring showed similar signs of fearfulness. And even when a new born mouse from this generation was raised by a mother and with other mice who were not fearful, that mouse still tended to be fearful as an adult. Now why is this? Well its thought that specific genes in an animals body have an influence on anxious behavior. These are genes that are associated with particular nerve-cell receptors in the brain. And the degree of overall of fearfulness in the mammal seems to depend in large part on the presence or absence of these nerve-cell receptors. And this appears to apply to humans as well by the way. But while a tendency towards anxiety and fear may well be an inherited trait, the specific form that the fear takes has more to do with the individuals environment. So a particular fear, like a fear of snakes or the fear of spider, say, is not genetic, but the overall tendency to have fearful responses, is.NO4:Lets turn our focus now to advertising. We all know what an advertisement is: Its essentially a message that announces something for sale. Now theres an important precondition that must exist before you have advertising, and thats a large supply of consumer goods, that is, things to sell. You see in a place where the demand for a product is greater than the supply, there is no need to advertise. Now the earliest forms of advertising going back many hundreds of years with a simple sign over shop doors that told you whether the shop was a bakery, a butcher shop or what have you. Then with the advent of printing, advertising increased substantially. As for products like coffee, tea and chocolate appeared in newspapers and other periodicals, as well as on the sides of building. In the American colonies, advertising and communication media like newspapers and pamphlets became a major factor in marketing goods and services. By modern standards, these early advertisements were quite small and subdued, not as splashy, whole page spread of today. Still some of them appeared on the front pages of newspapers probably because the news often consisted of less refresh reports from distant Europe while the news were current and local. Advertising really came and do it so and became an essential part of doing business during the industrial revolution. Suddenly there was a much greater supply of things to sell. And as we said earlier, that is the driving force behind advertising. Peoples attention had to be drawn to the new product. Lets take a look at some of the advertisements from that time.NO5:Moving away from newspapers, lets now focus on magazines. Now, the first magazine was a little periodical called The Review, and it was started in London in 1704. It looked a lot like the newspapers of the time. But in terms of its content, it was much different. Newspapers were concerned mainly with news events, but The Review focused on important domestic issues of the day as well as the policies of the government. Now in England at the time, people could still be thrown in jail for publishing articles that were critical of the king. And thats what happened to Daniel Defoe. He was the outspoken founder of The Review. Defoe actually wrote the first issue of The Review from prison. You see, he had been arrested because of his writings that criticized the policies of the Church of England, which was headed by the king. After his release, Defoe continued to produce The Review and magazine started to appear on a more frequent schedule, about three times a week, it didnt take long for other magazines to start popping up. In 1709, a magazine called The Tatler began publication. This new magazine contained a mixture of news, poetry, political analysis, and philosophical essays.NO6:The cattle ranching industry started in the new western United States in the late 1800s. As the industry developed, so did the horse riding contests that we called rodeos. Rodeos werent always the big entertainment shows that we see nowadays. The first ones were small contests started as a form of competition among people historically referred to as cowboys, although they did include both men and women. One duty of the cowboys was to guide herds of cattle from the grassy ranges into towns around the railroad lines where the cows were loaded onto trains. The cowboys would gather near these cow towns to compete for the unofficial title: best horse rider. They would demonstrate the riding skills they had learned as a matter of survival. The audience was composed mainly of other cowboys who watched the competitors critically since they knew what the events were all about. Rodeo contests took a different turn in the 1890s when organizers began to hold cowboy sports during yearly agricultural fairs. What was different was the audience. It consisted mostly of people who were unfamiliar with life on the range. They were amazed by the skill of the riders and the intelligence of the horses. Rodeo at agricultural fairs became so popular that ranchers and business people began to organize rodeos as independent events, separate from fairs. The organizers built large arenas and earned money by requiring spectators to pay for admission. One of the most notable rodeos of this type is still held annually in Wyoming. Its called Frontier Days. While Frontier Days is not the first independent rodeo, it is the annual show, taking place each year since 1897.NO7:Last week, you recall, we discussed the early development of railroads in the United States. Today I want to mention an even earlier form of transportation, one that brought the first European settlers to America. And thats the wooden sailing ship. From colonial times, sailing ships were vital to the economy. Many coastal towns depended on fishing or whaling for employment and income. This was especially true in the northeastern states. And there the wood from nearby forests and the skills of local designers and workers also formed the basis of an important shipbuilding industry. But the big profits were to be made on trade with faraway places. And since sea captains often became part of owners of their ships, they had a strong interest in the commercial success of their voyages. So these Yankees, thats what US sailors and officers came to be called, they carried on a very profitable trade with other parts of the world. The high point of this trade came in the mid-19th century with the introduction of the clipper ship, the enormous Yankee clippers with huge sails reaching nearly two hundred feet into the sky. Hed carry passengers and cargo from New York around South America to San Francisco in less than three months and clear to China in just half a year. At that time this seemed unbelievably fast and efficient. But in the 1860s, more reliable steam-powered ships began to take over. And soon the important role of sailing ships in the US economy would come to an end.NO8:Last time, we outlined how the Civil War finally got started. I want to talk today about the political management of the war on both sides, the north under Abraham Lincoln, and the south under Jefferson Davis. An important task for both of these presidents was to justify for their citizens just why the war was necessary. In 1861, on July 4th, Lincoln gave his first major speech in which he presented the northern reasons for the war. It was, he said, to preserve democracy. Lincoln suggested that this war was a noble crusade that would determine the future of democracy throughout the world. For him, the issue was whether or not this government of the people, by the people could maintain its integrity; could it remain complete and survive its domestic foes? In other words, could a few discontented individuals and by that he meant those who led the southern rebellion, could they arbitrarily break up the government and put an end to free government on earth? The only way for the nation to survive was to crash the rebellion. At the time, he was hopeful that the war wouldnt last long, and the slave owners would be put down forever. But he underestimated how difficult the war would be. It would be harder than any the Americans had thought before or since, largely because the north had to break the will of the southern people, not just by its army. But Lincoln rallied northerners to a deep commitment to the cause. They came to perceive the war as a kind of democratic crusade against southern society.NO9:Recently some anthropologists conducted an interesting case study in ethnology. Now ethnology, as you recall, is a branch of anthropology that deals with how various cultures develop and change. The study was about the development of basket weaving by African-American women who live in the town of Mount Pleasant, South Carolina. The town is known for its high quality sweet grass baskets which are woven by these women. Theyve been weaving the baskets for generations, handing down the skill from mother to daughter. Some of the baskets have been placed on permanent display at the Philadelphia Museum of Art. The origin of their basket weaving dates back to the 17th century and even earlier when these womens ancestors came to the United States from the west coast of Africa. Now, its mainly a hobby. But back in the 17th and 18th century, African American women wove the baskets for use on the rice plantations. There were two types of baskets then: workbasket and baskets for use in the home. The workbaskets were made out of bulrushes. Bulrushes are long, tough grass that grows in marshes. One type of workbaskets was the fan basket which was used to separate grains of rice from the waste. The baskets used in the homes were made out of more delicate sweet grass. They were used for everything from fruit baskets to baby cradles.NO10:In the late 1400s, when Christopher Columbus returned to Spain from the western hemisphere, he brought with him a sample of what the native Americans called maize, or, as we call it more often today, corn. The corn that Columbus introduced to Europe was the distant descendant of a grass native to Mexico. The peoples of the Americas probably started to domesticate this grass as early as 5000BC. After about a thousand years, they had developed a highly productive strand of corn which later became the basis for the great pre-Columbian civilizations. Figuratively speaking, both the cities of the Incas and the temples of the Mayas were built on corn. Domesticated corn and the people who cultivated it developed together. Without humans to care for it, domesticated corn could not survive. The kernels are crowded together beneath the strong protected husk and silk. And the young corn shoot is not strong enough to break through the husk on its own. If people did not strip away the husk and plant individual kernels, the corn would die out. NO11:W: Hello? M: Hi, Amy. This is Bill Johns. W: Oh. Hi, Bill. You werent in engineering class today, were you? M: I have the flu. I was wondering if you could tell me what went on. W: Actually we had an interesting class. Doctor Colin talked about a new type of fuel. M: Oh, yeah? W: Uh hum. Its called dimethyl ether or DME. M: Oh. I remember reading something about DME. Its mostly used in spray cans, right? W: Right. DME doesnt destroy the ozone so its been environmentally friendly. M: But doesnt DME pollute the air if its burned in an engine? W: No. Doctor Colin says something about its exhausts being clear that it doesnt release as many pollutants as diesel fuel. And he mentioned something about DME being more efficient than other alternative fuels. M: So when will it replace diesel fuel? W: Not for a while. Its not economical to mass produce. M: Well, thanks for the information. I guess I wont need to borrow your notes. W: Well, maybe you should look at them. We are having a test next week. M: Okay, could you give them to Mike Andrews? I think he is in your psychology class. He is my roommate. W: Sure. I hope youre feeling better soon. M: Thanks. Me too. Bye! W: Bye!NO12:W: Hi, Jim. What are you doing? M: Oh. Hi. Linda. Im working on a report on energy resources for my environmental science class. But Im having trouble finding enough information. W: You know we were talking about sources of fuel in my class today. M: Yeah? W: Prof Collins. He is all authority on energy sources. He was telling us about a new way of getting fuel oil from coal. M: I didnt know that was possible. W: He said something about coal being set on fire and blasted with a mixture of steam and oxygen. This process produces a gas made up of hydrogen and carbon, the, um, the basic elements of oil. M: And then they do something to change that gas to oil? W: Right. First. Since coal contains fewer hydrogen atoms than oil, they have to add some extra hydrogen to the gas. Then impurities are washed out with methanol. I think before this gas is sent on to reactors where its changed into oil. M: Since coal is so plentiful, I guess it wont be long till this new type of oil will be available all over the place, huh? W: I doubt it. Prof Collins said something about the process not being economically enough to use in this country. At any rate you really ought to talk to him. Hell be able to help you more than I can and hes got office hours all afternoon today. M: Thanks! Hes over in Anderson Hall, right? W: Right.NO13:Our electric car is the way of the future. Automobile manufactures are under the pressure to develop cars that do not pollute. One powerful motive is a California law requiring that by the year 2000, ten percent of the new car sales in the state be so-called zero-emission vehicles. These cars must put no pollutants whatsoever into the atmosphere. California is a huge market for the automobile companies, so they are working hard to meet these standards. So far the electric car seems to be the best alternative. So the biggest advantage of electric cars is that they dont pollute. However, they will be in competition with gas-powered cars. And thats where the weaknesses come out. The big problem is that the batteries in electric cars weigh a lot relative to the amount of power they deliver. For instance, in one electric car, the batteries weigh four hun