大学英语自学教程(中)

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1、大学英语自学教程(中)16-A. Heart Disease: Treat or Prevent?One of the greatest killers in the Western world is heart disease. The death rate from the disease has been increasing at an alarming speed for the past thirty years. Today in Britain, for example, about four hundred people a day die of heart disease.

2、 Western healthcare systems are spending huge sums of money on the surgical treatment of the disease.This emphasis on treatment is clearly associated with the technological advances that have taken place in the past ten to fifteen years. In this time, modern technology has enabled doctors to develop

3、 new surgical techniques and procedures. Many opeations that were considered impossible a few years ago are now performed every day in U.S. hospitals. The result has been a rapid increase in heart surgery.Although there is no doubt that a large number of people benefit from heart surgery, critics of

4、 our health-care systems point out that the emphasis on the surgical treatment of the disease has three clear disadvantages. First, it attracts interest and financial resources away from the question of prevention. Second, it causes the costs of general hospital care to rise. After hospitals buy the

5、 expensive equipment that is necessary for modern heart surgery, they must try to recover the money they have spent. To do this, they raise costs for all their patients, not just those patients whose treatment requires the equipment. The third disadvantage is that doctors are encouraged to perform s

6、urgery - even on patients for whom an operation is not at all necessary - because the equipment and surgical expertise is available. A federal government office recently said that major heart surgery was often per-formed even though its chances of success were low. In one type of heart surgery, for

7、example, only 15 percent of patients benefited from the surgery.In the recent past, medical researchers have begun to emphasize the fact that heart disease is associated with stress, smoking and a lack of exercise, and we can often reduce the risk of heart disease by paying more attention to these f

8、actors.More and more people are realizing that there is a connection between heart disease and the way they live. As a result of this new awareness, attitudes toward health are changing. In the past, people tended to think that it was sufficient for good health to have a good doctor who could be rel

9、ied on to know exactly what to do when they became ill. Now they are realizing that merely receiving the best treatment for illness or injury is not enough. They are learning that they must take more responsibility for their own health. Today many people are changing their dietary habits and eating

10、food with less fat and cholesterol. Many are paying more attention to reducing stress in their lives. The number of smokers in the United States is now far below the level of twenty years ago as many people succeed in breaking the habit and as fewer people take it up. More and more people are aware

11、of the benefits of regular exercise like walking, running, or swimming; some have begun to walk or ride bicycles to work instead of driving. Millions have become members of health clubs and have made health clubs one of the fastest growing businesses in the United States today. And now the beneficia

12、l effects of these changing attitudes and behaviors are beginning to appear: an encouraging decrease in deaths from heart disease.16-B. Dieting Four Way to HealthAlmost everyone considers going on a diet sometime in his or her life. All, regardless of sex and age, have something in common - losing w

13、eight and losing it fast.Though their common aim may seem basically good, they probably do not realize that misguided dieting can do more harm than good to their health. Going on too strict a diet can destroy the balance of chemicals in the human body. This happens because when the body is suddenly

14、given much less food than usual, it feels as though it is being attacked and tries hard to protect itself by saving energy. It does this by slowing down metabolism, the process by which the food we eat is converted into energy. As energy is supplied to the body at a slower and slower rate, dieters g

15、radually become so weak that they can do nothing. They soon lose interest in everything going on about them, and their resistance to illness becomes so low that they are easily attacked by one illness after another.Most of those who diet know that foods like rice, bread, potatoes, cakes, sweets, fru

16、its and some vegetables contain carbohydrates, and so can make one fat. What they do not realize, however, is that carbohydrates are our bodies main source of energy, and that these foods also contain components essential for the composition of substances that are needed to keep the body healthy. As

17、 a result, they try to avoid eating these foods, and consequently, they become weaker and less healthy. They begin to have difficulty sleeping properly and start to suffer from radical mood changes. In more serious cases, they even begin to show signs of mental illness.1t is strange enough that most

18、 strict diets recommend artificial sweeteners to take the place of sugar and other natural sweeteners. In fact, such artificial sweeteners actually increase ones appetite and lead to ones eating even more than usual.Of course, the fact that misguided forms of dieting result in so many problems does

19、not mean that no dieting is safe or all dieting is harmful to the health. Proper dieting can not only help a person lose ugly excess fat, but can also help him or her to keep it off and to lead a more active, happier and healthier life.You might ask just what a proper diet is. Well, simply expressed

20、, a proper healthy diet is one that is well-balanced, or, in other words, one that includes enough but not too many of the kinds of foods that provide the body with the nutrients that it needs to function properly. The most important of these nutrients are the macronutrients: proteins, carbohydrates

21、 and fats. The body needs fairly large amounts of proteins and carbohydrates for building material and energy. Meat, fish, eggs, milk, cream, and nuts all contain proteins and foods like rice, bread, potatoes, etc. contain carbohydrates. The body needs fat to keep it from the cold and to provide a p

22、rotective layer for the organs, but only in small quantities. Vitamins and minerals such as iron, calcium, are another group of essential nutrients, though the body does not need as great a quantity of these as it does the macronutrients - proteins, carbohydrates and fats.There are two types of vita

23、mins, water-soluble vitamins and fat-soluble vitamins. Water-soluble vitamins like vitamin C and the B-group vitamins do not stay in the body long and so foods containing these vitamins need to be taken rather often. On the other hand, the fat-soluble vitamins, vitamins A, D, E and K stay in the bod

24、y for long periods of time and so there is no need to take foods containing them so often.One way of getting enough nutrients while keeping ones weight down is to take substitutes for foods which contain too much fat. For example, instead of regular milk, one can take skimmed milk, which contains as

25、 many proteins and minerals as regular milk but has had the fat removed. In the same way, vegetable oil can be used for cooking instead of animal oil.17-A. Panic and Its EffectsOne afternoon while she was preparing dinner in her kitchen, Anne Peters, a 32-year-old American housewife, suddenly had se

26、vere pains in her chest accompanied by shortness of breath. Frightened by the thought that she was having a heart attack, Anne screamed for help. Her husband immediately rushed Anne to a nearby hospital where her pains were diagnosed as having been caused by panic, and not a heart attack.More and mo

27、re Americans nowadays are having panic attacks like the one experienced by Anne Peters. Benjamin Crocker, a psychologist at the University of Southern California, reveal that as many as ten million adult Americans have already experienced or will experience at least one panic attack in their lifetim

28、e. Moreover, studies conducted by the National Institute of Mental Health in the United States disclose that approximately 1.2 million adult individuals are currently suffering from severe and recurrent panic attacks.These attacks may last for only a few minutes; some, however, continue for several

29、hours. The symptoms of panic attacks bear such remarkable similarity to those of heart attacks that many victims believe that they are indeed having a heart attack.Panic attack victims show the following symptoms: they often become easily frightened or feel uneasy in situations where people normally

30、 would not be afraid; they suffer shortness of breath, experience chest pains, a quick heartbeat, sudden fits of trembling, a feeling that persons and things around them are not real; and most of all, a fear of dying or going crazy, A person seized by a panic attack may show all or as few as four of

31、 these symptoms.There has been a lot of explanations as to the causes of panic attacks. Many claim that psychological stress could be a logical cause, but as yet, no evidence has been found to support this theory. However, studies show that more women than men experience panic attacks and people who

32、 drink a lot as well as those who use drugs are more likely to suffer attacks.It is reported that there are at least three signs that indicate a per-son is suffering from a panic attack rather than a heart attack. The first is age. People between the ages of 20 and 30 are more often victims of panic

33、 attacks. The second is sex. More women suffer from recurrent panic attacks than men. The third is the multiplicity of symptoms. A panic attack victim usually suffers at least four of the previously mentioned symptoms, while a heart attack victim often experiences only pain and shortness of breath.I

34、t is generally agreed that a panic attack does not directly endanger a persons life. All the same, it can unnecessarily disrupt a persons life by making him or her so afraid of having a panic attack in a public place that he or she may refuse to leave home and may eventually become isolated from the

35、 rest of society. Dr. Crockers advice to any person who thinks he is suffering from a panic attack is to consult a doctor for a medical examination to rule out the possibilities of physical illness first. Once it has been confirmed that he or she is, in fact, suffering from a panic attack, the victi

36、m should seek psychological and medical help.17-B. Sleepwalking ?Fact or Fancy?There is an endless supply of stories about sleepwalkers. Persons have been said to climb on roofs, solve mathematical problems, compose music, walk through windows, and commit murder in their sleep.In Revere, Massachuset

37、ts, a hundred policemen searched for a lost boy who left his home in his sleep and woke up five hours later on a strange sofa in a strange living room, with no idea how he had got there.At the University of Iowa, a student was reported to have the habit of getting up in the middle of the night and w

38、alking three-quarters of a mile to the Iowa River. He would take a swim and then go back to his room to bed.An expert on sleep in America claims that he has never seen a sleepwalker. He is said to know more about sleep than any other living man, and during the last thirty-five years has lost a lot o

39、f sleep watching people sleep. Says he, of course, I know that there are sleepwalkers because I have read about them in the newspapers. But none of my sleepers ever walked, and if I were to advertise for sleepwalkers for an experiment, I doubt that Id get many takers. Sleepwalking, nevertheless, is

40、a scientific reality. It is one of those strange phenomena that sometimes border on the fantastic. What is certain about sleepwalking is that it is a symptom of emotional disturbance, and that the only way to cure it is to remove the worries and anxieties that cause it. Doctors say that sleepwalking

41、 is much more common than is generally supposed. Many sleepwalkers do not seek help and so are never put on record, which means that an accurate count can never be made.The question is: Is the sleepwalker actually awake or asleep? Scientists have decided that he is about half-and-half. Dr. Zelda Tep

42、litz, who made a ten-year study of the subject, says, The sleepwalker is awake in the muscular area, partially asleep in the sensory area.” In other words, a person can walk in his sleep, move around, and do other things, but he does not think about what he is doing.What are the chances of a sleepwa

43、lker committing a murder or doing something else extraordinary in his sleep? Dr. Teplitz says, Most people have such great inhibitions against murder or violence that they would awaken if someone didnt wake them up. In general, authorities on sleepwalking agree with her. They think that people will

44、not do anything in their sleep that is against their own moral standard. As for the publicized cases, Dr. Teplitz points out, Sleepwalking itself is dramatic. sleepwalkers can always find an audience. I think that some of their tall tales get exaggerated in the telling.” In her own records of case h

45、istories, there is not one sleepwalker who ever got beyond his own front door.To protect themselves, some sleepwalkers have been known to tie themselves in bed, lock their doors, hide the keys, bolt the window, and take all sorts of measures to wake themselves if they should get out of bed. Curiousl

46、y enough, they have an unusual way of avoiding their own traps when they sleepwalk, so none of their tricks seem to work very well. Some sleepwalkers talk in their sleep loudly enough to wake someone else in the family who can then shake them back to their senses. Children who walk in their sleep us

47、ually outgrow the habit. In many adults, too, the condition is more or less temporary. If it happens often, however, the sleepwalker should seek help. Although sleepwalking itself is nothing to become alarmed about, the problems that cause the sleepwalking may be very serious.18-A. Why Are Maps Draw

48、n with North at the Top?Now it is hard to visualize a map that does not feature north at the top, but this was not always so.The oldest known map in the accepted sense of the word was drawn about 3, 800 BC, and represents the river Euphrates flowing through northern Mesopotamia, Iraq. This, and othe

49、rs that followed it, were little more than rough sketches of localized features; it was not until many centuries later that the ancient Greeks placed the science of map-making on a sound footing.At the forefront of the pioneers in the field was the Greek mathematician and philosopher Claudius Ptolem

50、aeus (c. AD 90 ?168), more popularly known to history as Ptolemy. The last great scientist of the classical period, he was the first to draw a map that was based on all available knowledge, rather than guess or imagination. Earlier, the Bahylonians had attempted to map the world, but they presented

51、it in the form of a flattened disc rather than a sphere, which was the form adopted by Ptolemy.Given the state of knowledge of those times, he got things wrong; for example, his estimate of China and the Atlantic Ocean was far from being accurate. Nevertheless, it was a useful effort, and the map re

52、mained a work of reference for over a thousand years. In fact, Christopher Columbus used a version of it when he set sail in search of the New World - which caused him some navigational problems, since Ptolemy had calculated wrongly the size of the Atlantic and was unaware that the Pacific Ocean exi

53、sted.The really important thing about Ptolemys map was that north was at the top. The reason for this was that he decided to orientate the map in the direction of the Vole Star since Polaris was the immovable guiding light in which the voyagers of that era placed their trust.North at the top remaine

54、d the accepted arrangement until the early Middle Ages, when the Church began to interfere seriously with the advance of science. In accordance with the orders of the Church, maps were still produced in accordance with Ptolemys principles ?but now Jerusalem was the central feature, as it was held to

55、 be the center of the Christian faith, and east was moved to the top.These maps are often called T Maps because they show only three continents - Europe, Asia and Africa - separated by the T formed by the Mediterranean Sea and the River Nile. From a navigational point of view, they were almost usele

56、ss.More accurate maps began to appear in the 14th century, with the spread of trade and increasing reliance on the compass. Once again, north assumed its rightful place at the top of maps.18-B. You Have a ChoiceTwo trains are traveling side by side and at the same speed along parallel tracks. We are

57、 seated in one of the trains, and with us we have a special speedometer that measures their relative speech. Since the trains are traveling at the same speed, their relative speed is zero; the speedometer therefore reads 0.Suddenly the other train seems to start pulling ahead of ours. The speedomete

58、r shows a reading of 10 miles per hour. The other train has apparently increased its speed. Hut can we he absolutely certain of this increase?If your answer is yes, you are wrong. You are wrong because all that we know is that the relative speed between the two trains changed from 0 mph to 10 mph. N

59、othing more. This change could have been brought about in one of two ways:1. The other train increased its speed.2. Our train decreased its speed.There are thus two possible explanations to account for the change in speed, but we dont know which one is right. Furthermore, regardless of which explana

60、tion we choose, the end result will he the same: the other train will arrive at the station first. So it makes no difference whether we say that the other train increased its speed or that our train decreased its speed.Since both explanations lead to the same result, you can choose either one. Whene

61、ver two things are relative, you can choose either one of them. The converse is also true: whenever you have a choice between two things that are equally possible, then the things are relative. There is no reason, except convenience, for choosing one explanation over the other. The relative speed be

62、tween the trains remains the same, 10 mph; and the end result will be the same.Now let抯 suppose that both trains are at the railroad station loading and unloading passengers and baggage. A half-hour passes. As we look at the other train through our window, we see that our train seems to start moving

63、, smoothly and slowly. For a minute or so, our train seems to travel at a uniform speed. Our special speedometer shows that the relative speed between the two trains is 20 mph. But as we look out our window, we suddenly see the last coach of the other train disappear from sight and notice the motion

64、less station behind it. So we are not moving after all. The other train has been moving!This peculiar and often frustrating experience is an effect of relative motion. At the train station we cannot tell whether it was our train that changed its speed from 0 mph to 20 mph or whether it was the other

65、 train that changed its speed from 0 mph to 20 mph. Only after the other train pulled out of the station could we see that it, and not our train, was moving.Now let us again raise the question that was raised at the beginning of this article: can we be absolutely certain that the other train did ind

66、eed increase its speed, and in this case pull out of the station?If your answer is yes, then you are wrong again. All we can be certain of is that the relative speed between the two trains changed.These examples illustrate an important principle in the special theory of relativity. If A appears to be moving at a steady speed relative to B, we cann