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听力原文： In the United States, couples usually receive gifts from their relatives and friends when they get married. Sometimes a bride will exchange a gift for something else if she doesn't find it useful. We give gifts to express our good wishes for the marriage, but gifts aren't necessary for the marriage itself. However, in some societies gifts are very important, and the marriage isn't legal without them. One type of gift is called bride service. A young husband must work for his wife's family. He may work for as long as fifteen years or until the third child is bom. Bride service may seem strange to us, but it is necessary in societies where people don't have money or material things to exchange at marriage.
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In an El Nino, the winds pushing the water around get weaker. As a result, some of the warm water piled up in the west slumps back down to the east, and not as much cold water gets pulled up from below.
What is an El Nino
An El Nino is a temporary change in the climate of the Pacific Ocean, in the region around the equator. You can see its effects in both the ocean and atmosphere, generally in Northern Hemisphere winter. Typically, the ocean surface warms up by a few degrees Celsius. At the same time, the place where strong thunderstorms occur on the equator moves eastward. Although those might seem like small differences, it nevertheless can. have big effects on the world's climate.
What muses it？
Usually, the wind blows strongly from east to west along the equator in the Pacific. This actually piles up water (about half a meter's worth) in the western part of the Pacific. In the eastern part, deeper water (which is colder than the sunwarned surface water) gets pulled up from below to replace the water pushed west. So, the normal situation is warm water (about 30 ℃; ) in the west, cold (about 22℃ ) in the east. In an El Nine, the winds pushing that water around get weaker. As a result, some of the warm water piled up in the west slumps hack down to the east, and not as much cold water gets pulled up from below. Both these tend to make the water in the eastern Pacific warmer, which is one of the signs of an El Nine. But it doesn't stop there. The warmer ocean then affects the windsit makes the winds weaker! So if the winds get weaker, then the ocean gets warmer, which makes the winds get weaker, which makes the ocean get warmer... This is called a positive feedback, and is what makes an El Nino grow.
So what makes it stop growing？
The ocean is full of waves, but you might not know how many kinds of waves there are. There's one called a Rossby wave that is quite unlike the waves you see when you visit the beach. It is more like a distant cousin to a tidal wave. The difference is that a tidal wave goes very quickly, with all the water moving pretty much in the same direction. In a Rossby wave, the upper part of the ocean, say the top 100 meters or so, will be leisurely sliding one way, while the lower part, starting at 100 meters and going on down, will be slowly moving the other way. After a while they switch directions. Everything happens very slowly and inside the ocean, and you can't even see them on the surface. These things are so slow; they can take months or years to cross the oceans. If you had the patience to sit there while one was going by, you'd hardly notice it; the water would be moving 100 times slower than walking speed. But they are large, hundreds or thousands of kilometers in length (Not height! Remember, you can hardly see them on the surface), so they can have an effect on things. Another wave you rarely hear about is called a Kelvin wave, and it had some characteristics in common with Rosaby waves, but is somewhat faster and can only exist closer to the equator (say, within about 5 degrees of latitude around the equator).
El Ninos often start with a Kelvin wave spreading from the western Pacific over towards South America. Perhaps you saw, on the TV news, the movie (produced by JPL) for the El Nine of 1997/98？ It showed a whitish blob(白色团状物) (indicating a sea level some centimeters higher than usual) moving along the equator from Australia to South America. That is one of the hallmarks of a Kelvin wave, the early part of the El Nino process.
When an El Nino gets going in the middle or eastern part of the Pacific, it creates Rossby waves that drift slowly towards Southeast Asia. After several months of traveling, they finally get near the coast and reflect back. The changes in interior ocean temperature that these waves carry with it "cancel out" the original temperature changes that made the El Nino in the first place. The main point is that it shuts off when these funny interiorocean waves travel all the way ever to the coast of Asia, get reflected, and travel hack, a process that can take many months.
What effects does i
A strong El Nino is often associated with wet winters over the southern U.S., as well as drought in Indonesia, Philippines and Australia.
听力原文： Education is required and free for every child in the United States. Most children start by the age of six. They attend eight years of elementary school and four years of high school (or secondary school). The money for free public schools comes from taxes, and each state is responsible for its own educational system. State legislatures set the educational requirements but leave the management of the schools in the hands of the local communities. Most states require their children to go to school until a certain age. This age varies form. 16 to 18 according to the laws of the individual states. The Federal Government contributes funds to the states for additional school services.
After graduation from the high school, a student can start his higher education in a twoyear college, a fouryear college, a university, or a specialized professional school either public or private. Most colleges admit students on the basis of their high school records. The cost of the college education is great in private universities, but it is much less in those supported by states and cities. Many students receive scholarships' form. the schools, the Government, or private foundations and organizations. More than 50% of the college students work to help pay their college expenses. Only 2% of the population of the country cannot read and write.
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