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It’s in the CardsIn recent years, more and more people have been paying for things with credit cards. There are now 565 million credit cards worldwide, but it doesn’t stop there. Debit cards (电子记账卡) are being issued by banks, and store cards are being offered by many department stores. Bills and coins are gradually being replaced by "plastic money." In many countries, phone cards have been introduced for people to use in pay phones. In addition, cards made of paper are being replaced by plastic ones by many organizations and clubs. For example, if you belong to a sports club, your membership card may well be made of plastic.How safe is the plastic used to make these cards, though Until now, most cards have been made from a plastic called PVC. While PVC is being produced, harmful chemicals are released into the atmosphere. One of the most dangerous chemicals that is released is dioxin, which is known to cause cancer in humans. A further problem is that, when a PVC card is thrown away, it is not biodegradable; this means that it does not "break down" and cannot be recycled. Obviously, recycling reduces pollution of the environment.The executive director of the environmental organization and charity Greenpeace, Peter Melchett, says, "If there is a solution to this-and an alternative then it would be madness not to use it." Greenpeace has found a solution and an alternative. Their new credit card is made entirely from a biodegradable plastic that uses plants. The card breaks down in around three months in soil; in this way, it is recycled. In contrast, a PVC card lasts for centuries. Greenpeace hopes that many organizations will soon follow their example and issue cards that do not threaten the public health. Most credit cards are biodegradable.()
Dreams of FlightThe story of man’s dream of flight, of his desire to reach the stars, is as old as mankind itself. According to Greek legend, Daedalus was the first man to fly. He and his son had been kept on an island, in order to escape, Daedalus shaped wings of wax (蜡) into which he stuck bird feathers. During their flight, his son flew too high and the sun melted the wax. He was drowned in the sea. The father was supposed to have continued his Night and reached Sicily, several hundred miles away.There is also an English legend of King Bladud who, during his rule in the ninth century B.C., used wings to fly. But his flight was short-lived and he fell to his death. The dream of flying continued, but in all the legends, the flier rose like a bird only to fall like a stone. It took hundreds of years that men flew up into the air and returned to earth safely.The first man to approach flying on a scientific basis was an Englishman who lived during the thirteenth century. He looked at the air about us as a sea, and he believed that a balloon could float on the air just as a boat did on water. Almost four hundred years later, an Italian priest applied his principle of air flight. He designed a boat, which would be held in the air by four hollow spheres (空心球). Each of the four balls was to be 20 feet in diameter (直径) and made of very thin copper. But his boat was never .built since it was not possible to make spheres of such thin metal and such size in those days.After studying the flight of birds and the movement of the air, a great scientist of the fifteenth century concluded that birds flew because they flapped (摆动) their wings and that it was possible for man to do the same. So a kind of flapping-wing flying machine was invented. Many men tried and failed to fly with flying machines. It was not until 1890 that people discovered why this method would never succeed-man could not develop sufficient power with his arms and legs. According to the last paragraph, man could not fly with flapping-wing flying machines because()
Flying the Hypert Skies A little airplane has given new meaning to the term "going hyper. " The Hyper-X recently broke the record for air-breathing jet planes when it traveled at a hypersonic speed of seven times the speed of sound. That’s about 5,000 miles per hour. At this speed, you’d get around the world -- flying along the equator (赤道) -- in less than 5 hours. The Hyper-X is an unmanned,experimental aircraft just 12 feet long. It achieves hypersonic (超音速的) speed using a special sort of engine known as a scramjet. It may sound like something from a comic book,but engineers have been experimenting with scramjets since the 1960s. For an engine to burn fuel and produce energy, it needs oxygen. A jet engine, like those on passenger airplanes, gets oxygen from the air. A rocket engine typically goes faster but has to carry its own supply of oxygen. A scramjet (紧急刹车) engine goes as fast as a rocket, but it doesn’t have to carry its own oxygen supply. A scramjet’s special design allows it to obtain oxygen from the air that flows through the engine. And it does so without letting the fast-moving air put out the combustion (燃烧) flames. However, a scramjet engine works properly only at speeds greater than five times the speed of sound. A booster rocket carried the Hyper-X to an altitude of about 100,000 feet for its test flight. The aircraft’s record-beating flight lasted just 11 seconds. Although the little plane’s self-powered flight lasted only 11 seconds, that brief journey on March 27 makes a major milestone on the way to a new breed of very fast airplanes, comments Werner J. A. Dahm of the University of Michigan in Ann Arbor. In the future, engineers predict, airplanes equipped with scramjet engines could transport cargo quickly and cheaply to the brink of space. Such hypersonic jets could potentially carry passengers anywhere in the world in just a few hours. Out of the three experimental Hyper-X aircrafts built for NASA, only one is now left. The agency has plans for another 11-second hypersonic flight, this time at 10 times the speed of the sound. What is NOT true about the scramjet engine
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