单选题Ann Curry is a famous news presenter of the NBC News "Today" show. When she was 15 she happened to walk into a bookstore in her hometown and began looking at the books on the shelves. The man behind the counter, Mac McCarley, asked if she'd like a job. She needed to start saving for college, so she said yes. Ann worked after school and during summer vacations, and the job helped pay for her first year of college. During college she would do many other jobs: she served coffee in the student union (学生会), was a hotel maid and even made maps for the U.S. Forest Service. But selling books was one of the most satisfying jobs. One day a woman came into the bookstore and asked Ann for books on cancer (癌 症). The woman seemed anxious. Ann showed her practically everything they had and found other books they could order. The woman left the store less worried, and Ann has always remembered the pride she felt in having helped her customer. Years later, as a television reporter in Los Angeles, Ann heard about a child who was born with problems with his fingers and his hand. His family could not afford a surgical (外科的) operation, and the boy lived in shame, hiding his hand in his pocket all the time. Ann persuaded her boss to let her do the story. After the story was broadcast, a doctor and a nurse called, offering to perform the surgical operation for free. Ann visited the boy in the recovery room after the operation. The first thing he did was to hold up his repaired hand and say, "Thank you." What a sweet sense of satisfaction Ann Curry felt! At McCarely's bookstore, Ann always sensed she was working for the customers, not the store. Today it's the same. NBC News pays her, but she feels as if she works for the people who watch the programs, helping them make sense of the world.

单选题Questions 15-18

单选题In the atmosphere, carbon dioxide acts rather like a one-way mirror—the glass in the roof of a greenhouse which allows the sun's rays to enter but prevents the heat from escaping. According to a weather expert's prediction, the atmosphere will be 3 ℃ warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate. If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several meters and severely flooding coastal cities. Also. the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of earth's chief food-growing zones. In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming, in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels. Satellite pictures show that large areas of Antarctic ice are already disappearing. The evidence available suggests that a warming has taken place. This fits the theory that carbon dioxide warms the earth. However, most of the fuel is burnt in the northern hemisphere, where temperatures seem to be falling. Scientists conclude, therefore, that up to now natural influences on the weather have exceeded those caused by man. The question is: Which natural cause has most effect on the weather? One possibility is the variable behavior of the sun. Astronomers at one research station have studied the hot spots and "cold" spots (that is, the relatively less hot spots) on the sun. As the sun rotates, every 27.5 days, it presents hotter or "colder" faces to the earth, and different aspects to different parts of the earth. This seems to have a considerable effect on the distribution of the earth's atmospheric pressure, and consequently on wind circulation. The sun is also variable over a long term: its heat output goes up and down in cycles, the latest trend being downward. Scientists are-now finding mutual relations between models of solar-weather interactions and the actual climate over many thousands of years, including the last Ice Age. The problem is that the models are predicting that the world should be entering a new Ice Age and it is not. One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia of the earth's climate. If this is tight, the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun's diminishing heat.

单选题Whatwasthemandoing?[A]Lookingforawatchforhismother.[B]Lookingforanecklaceforhismother.[C]Lookingforabirthdaygiftforhismother.

单选题Questions 27-30

单选题 The world seems to be going diet crazy, and yet our nation's obesity rate has shot up year after year. And, it's not only the over 20 population that has to worry about their weight anymore. Children from kindergarten to twelfth grade are also experiencing the problems of an overweight lifestyle. According to the website cosmiverse.com, 11% of adolescents are categorized as being over-weight, and another 16% are in danger of becoming overweight. This is a 60% jump from the 1980's. Some of the blame is being put on schools wanting to fit more academic classes into the children's schedule rather than waste time on physical education. This new take on education has left us with physical activity at an all-time national low, resulting in obesity and poor physical conditioning at an all-time national high. The schools have tried a few solutions; the most recent in the news has been taking soda out of schools and increasing the required time children must be active during school. Will those methods help at all? Education is important at school, but starts at home. I believe students are getting their bad habits from watching their parents and how they eat and exercise. The school system only helps to hinder the child's dietary eating. I know there are studies showing genes that determine how a child will be built. That does not explain however, why the rate continues to increase at such a rapid rate each year. It seems more likely that more and more families have both parents working, leaving their children to their own means for a meal. "Nintendo, TV, Playstation and the like," are what Physical Education teacher, Sue Arostegui, attributes the inactiveness to. "Parents are either gone or too scared with today's society to let them out and play." Classes on health need to become more regular and sports need to be encouraged. At Live Oak High School the staff does a good job of teaching how to eat and exercise to stay healthy. The freshmen study health every Wednesday in RE., and Para James teaches healthy eating and food preparation in Home Economics for the first few weeks of every school year. "Kids have no idea how many calories they are eating," said James of the overweight problems facing students. "Fast food is becoming more popular, it's easier and parents are busy. They are only setting their kids up to gain weight with that diet however." School cafeterias are also getting blamed for the students' eating habits. "Healthy eating should start at home," said L.O.H.S. cafeteria cool Brenda Myers. "Too many kids are being raised on fast food. After eating so much fast food they don't have any tastes for real home cooked food. I always have healthy foods for students, but they are less likely to eat them." Other schools do not even have the type of programs Live Oak offers and are suffering even worse consequences. Sports keep students fit and healthy. There need to be more readily available sports programs for anyone who would like to join. Many students when they feel they do not meet the standards for a team will admit defeat and drop off the team: There needs to be a program that all students will be interested in and continue through for the entire season. Schools can only do and be blamed for so much however, and it will be up to the parents to become more aware of what activities their children are participating in and how healthy they are eating. Until that happens, I foresee the obesity rate continuing on its uphill curve.

单选题The ancient Chinese board game Go was invented long before there was any writing to record its rules. A game from the impossibly distant past has now brought us closer to a moment that once seemed part of an impossibly distant future: a time when machines are cleverer than we are. For years, Go was considered the last redoubt against the march of computers. Machines might win at chess, draughts, Othello, Monopoly, bridge and poker. Go, though, was different. The game requires intuition, strategising, character reading, along with vast numbers of moves and permutations. It was invented to teach people balance and patience, qualities unique to human intelligence. This week a computer called AlphaGo defeated the world"s best player of Go. It did so by "learning" the game, crunching through 30 million positions from recorded matches, reacting and anticipating. It evolved as a player and taught itself. That single game of Go marks a milestone on the road to "technological singularity", the moment when artificial intelligence becomes capable of self-improvement and learns faster than humans can control or understand. Fear of the super-intelligent, over-mighty machine is embedded in our psyche. Technological advance brings with it the anxiety that the machines will eventually threaten humanity, a dread underpinned by the attribution to machines of our own evolutionary instinct to survive at the expense of lesser species. Artificial intelligence is advancing in ways that were once the preserve of science fiction. Scientists are competing to build robot footballers, with a prediction that would once have sounded barmy: "By the middle of the 21st century, a team of fully autonomous humanoid robot soccer players shall win a soccer game, against the winner of the most recent World Cup." Pepper, an affectionate humanoid robot, was unveiled last year. It is designed to "make people happy" by reading human emotions using a 3D depth sensor and lasers which analyse the facial expressions and voice tones of the people around it. Robot comes from the Czech robota meaning forced labour. Machines are increasingly working with humans. They even make financial decisions, one Hong Kong firm recently appointed an algorithm to its board, with an equal vote on investment decisions. Entrenched in our culture is the idea that when Man overreaches himself by playing God, he faces disaster. In Mary Shelley"s Frankenstein , the monster made by man is an offence against religion and nature that turns on its creator. Its alternative title was The Modern Prometheus ; a reference to the figure from Greek mythology who was punished for displaying arrogance towards the gods. It is a short step from Frankenstein to HAL, the softly spoken computer in 2001: A Space Odyssey, which also turns on its human masters. The film Ex Machina is the latest expression of that terror. Underlying this staple sci-fi plot is the assumption that a machine with comparable or greater abilities than ours will inevitably become an enemy. The theory goes that a robot will eventually take over and throw off the "forced labour" reflected in its name. Yet machines do only what they are created to do, and no robot could be built that shares our evolutionary biology. For AlphaGo to represent a danger, it would have to know that it had won, and to like winning. As drone technology shows, intelligent machines can be programmed to endanger humans. All inventions can be turned to nefarious ends, and the advance of artificial intelligence requires human intelligence to frame a set of robotic ethics. While the machines do not need regulation, the people who invent and use them do. In 1942, the great science fiction writer Isaac Asimov drew up three laws governing robot behavior: 1. Never harm a human being through action or inaction; 2. Obey human orders (subject to rule 1); 3. A robot must protect its own existence, (subject to t and 2). It is no accident that Asimov"s code was drawn up at a time when unfettered power, based on Superior technology, was causing untold suffering across the world. He later added a fourth: that robots should not allow humanity in general to come to harm. To Asimov"s rules might be added requirements to comply with existing international law and human rights, to design robots in a way that their function is clear and apparent, and to ensure that human beings bear direct legal responsibility for robot behavior. A code of ethics for roboticists would be complex, but no harder to frame than the regulations governing existing relationships between man and machines: speed limits, safety rules, arms treaties. Drawing up the new robot laws would require patience, foresight and adaptability: the very human qualities to be instilled when Go was invented.

单选题

单选题The timing of market entry is critical to the success of a new product. A company has two alternatives: it can compete to enter a new product market first—otherwise known as "pioneering"—or it can wait for a competitor to take the lead, and then follow once the market has been established. Despite the limitations of existing research, nobody denies that there are advantages to being a pioneering company. Over the years, there has been a good deal of evidence to show a performance advantage for pioneers. For many new products, customers are initially unsure about the contribution of product characteristics and features to the products" value. Preferences for different characteristics and their desired levels are learned over time. This enables the pioneering company to shape customer preferences in its favour. It sets the standard to which customers refer in evaluating followers" products. The pioneering product can become the classic or "original" product for the whole category, opening up a flood of similar products onto the market, as exemplified by Walkman and Polaroid. The pioneering product is a bigger novelty when it appears on the market, and is therefore more likely than those that follow to capture customer and distributor attention. In addition, a pioneer"s advertising is not mixed up with competitors" campaigns. Even in the long term, followers must continue to spend more on advertising to achieve the same effect as pioneers. The pioneers can set standards for distribution, occupy the best locations or select the best distributors, which can give them easier access to customers. For example, in many US cities the coffee chain Starbucks, as the first to market, was able to open coffee bars in better known locations than its competitors. In many industrial markets, distributors are not keen to take on second and third products, particularly when the product is technically complex or requires large inventories of spare parts. "Switching costs" arise when investments are required in order to switch to another product. For example, many people have developed skills in using the traditional "qwerty" keyboard. Changing to the presumably more efficient "dvorak" keyboard would require relearning how to type, an investment that in many cases would exceed the expected benefits in efficiency. Switching costs also arise when the quality of a product is difficult to assess. People who live abroad often experience a similar "cost" when simple purchase decisions such as buying detergent, toothpaste or coffee suddenly become harder because the trusted brand from home is no longer available. Pioneering products have the first chance to become this trusted brand. Consequently, the companies that follow must work hard to convince customers to bear the costs and risks of switching to an untried brand of unknown quality. Unlike other consumer sectors, the value to customers of many high technology products relies not only on their features but also on the total number of users. For example, the value of a videophone depends on the number of people using the same or a compatible system. A pioneer obviously has the opportunity to build a large user base before competitors enter the market. This reduces followers" ability to introduce differentiated products. There are other advantages of a large user base, such as the ability to share computer files with other users. Thus, software companies are often willing to give away products to build the market quickly and set a standard.

单选题Women's minds work differently from men's. At least, that is what most men are convinced of. Psychologists view the subject either as a matter of frustration or a joke. Now the biologists have moved into this minefield, and some of them have found that there are real differences between the brains of men and women. But being different, they point out hurriedly, is not the same as being better or worse. There is, however, a definite structural variation between the male and female brain. The difference is in a part of the brain that is used in the most complex intellectual processes—the link between the two halves of the brain. The two halves are linked by a trunkline of between 200 and 300 million nerves, the corpus callosum. Scientists have found quite recently that the corpus callosum in women is always larger and probably richer in nerve fibers than it is in men. This is the first time that a structural difference has been found between the brains of women and men and it must have some significance. The question is "What?", and if this difference exists, are there others? Research shows that present-day women think differently and behave differently from men. Are some of these differences biological and inborn a result of evolution? We tend to think that is the influence of society that produces these differences. But could we be wrong? Research showed that these two halves of the brain had different functions, and that the corpus callosum enabled them to work together. For most people, the left half is used for word-handling, analytical and logical activities; the right half works on pictures, patterns and forms. We need both halves working together. And the better the connections, the more harmoniously the two halves work. And, according to research findings, women have the better connections. But it isn't all that easy to explain the actual differences between skills of men and women on this basis. In schools throughout the world girls tend to be better than boys at "language subjects" and boys better at maths and physics. If these differences correspond with the differences in the hemispheric trunkline, there is an unalterable distinction between the sexes. We shan't know for a while, partly because we don't know of any precise relationship between abilities in school subjects and the functioning of the two halves of tile brain, and we cannot understand how the two halves interact via the corpus callosum. But this striking difference must have some effects and, because the difference is in the parts of the brain involved in intellect, we should be looking for differences in intellectual processing.

单选题 It looks unlikely that medical science will abolish the process of ageing. But it no longer looks impossible. "In the long run," as John Maynard Keynes observed, "we are all dead." True. But can the short run be {{U}}elongated{{/U}}in a way that makes the long run longer? And if so, how, and at what cost? People have dreamt of immorality since ancient times. Now, with the growth of biological knowledge that has marked the past few decades, a few researchers believe it might be within reach. To think about the question, it is important to understand why organisms — people included —age in the first place. People are like machines, they wear out. That much is obvious. However, a machine can always be repaired. A good mechanic with a stock of spare parts can keep it going indefinitely. Eventually, no part of the original may remain, but it still carries on, like Lincoln's famous axe that had three new handles and two new blades. The question, of course, is whether the machine is worth repairing. It is here that people and nature disagree. Or, to put it slightly differently, two bits of nature disagree with each other. From the individual's point of view, survival is an imperative. A fear of death is a sensible evolved response and, since ageing is a sure way of dying, it is no surprise that people want to stop it in its tracks. Moreover, even the appearance of ageing can be harmful. It reduces the range of potential sexual partners who find you attractive and thus, again, curbs your reproduction. The paradox is that the individual's evolved desire not to age is opposed by another evolutionary force, the disposable soma. The soma is all of a body's cells apart from the sex cells. The soma's role is to get those sex cells, and thus the organism's genes, into the next generation. If the soma is a chicken, then it really is just an egg's way of making another egg. And if evolutionary logic requires the soma to age and die in order for this to happen, so be it. Which is a pity, for evolutionary logic does, indeed, seem to require that. The argument is this. All organisms are going to die of something eventually. That something may be an accident, a fight, a disease or an encounter with a hungry predator. There is thus a premium on reproducing early rather than conserving resources for a future that may never come. The reason why repairs are not perfect is that they are costly and resources invested in them might be used for reproduction instead. Often, therefore, the body's mechanics prefer lash-ups to complete rebuilds — or simply do not bother with the job at all. And if that is so, the place to start looking for longer life is in the repair shop.

单选题Questions 27—30

单选题Valentine"s Day is tomorrow, and we are all thinking about true love and heart-shaped chocolate candy. Well, maybe not all of us. Some of us, actually, are considering the quantifiable aspects of divorce. In America today, some 50 percent of marriages are predicted to end in divorce. And at the University of Washington in Seattle they say they can tell you exactly—well, almost exactly—which ones those will be. A psychologist, a mathematician, and a pathologist have devised what they call a proven mathematical formula for detecting which relationships will go sour—thereby holding out hope that such couples can overcome their problems, and avoid divorce. "We have been able to predict that divorce will happen before [it does]. That"s old news," says John Gottman, emeritus professor of psychology. "But what we have now is a scientific model for understanding why we can predict it with such accuracy." The work marks the first time a mathematic model is being used to understand such deep personal human interactions, adds James Murray, professor of applied mathematics. "It is totally objective. And our prediction of which couples would divorce within a four-year period was 94 percent accurate." This is how it works. Couples face each other and discuss—each speaking in turn—a subject over which they have disagreed more than once in the past. They are wired to detect various physiological data, such as pulse rates, and they"re also videotaped. A session lasts a mere 15 minutes. The research team watches and analyzes the tapes and data, awarding plus or minus points depending on the type of interactions and according to a standard scoring system. Everything is then translated into equations and plotted on a graph, which the researchers have dubbed the "Dow- Jones Industrial Average for marital conversation". Once this is done, different situations are simulated and analyzed from the equations and graphs, and predictions are made. Over the past 16 years more than 700 couples (at different stages of their marriages) took part in the research. But let"s go back a moment. It all starts, say, with a chat about mothers-in-law—apparently one of the hot topics of contention among couples, along with money and sex, according to Dr. Murray. "The husband might say to his wife, "Your mother really is a pain in the neck." Well, that"s a minus two points. A shrug, that"s a no-no—so minus one. And rolled eyes—very negative, that"s minus two." If however, the husband were to say, "Your mother is a pain in the neck ... but she is sometimes funny," then, according to the researchers, you would take away two points and then give one back. If the husband cracked a smile, he would get another point. At the end of all the additions and subtractions, a stable marriage is indicated by having five more positive points than negative ones. Otherwise, warns the team, the marriage is in trouble. In trouble—but not doomed. The whole point of the model, says Dr. Gottman, is that it gives therapists new understanding with which they can help couples overcome patterns of interaction and prevent divorce. "What we are suggesting," says Murray, "is that couples who take this experiment then be told the prediction and realize they are going to have to both change their behavior and repair what is wrong." Not everyone buys into this model. Bonnie Jacobson, a clinical psychologist and processor at New York University, says it is "absolutely impossible" to understand the workings of a relationship via a one-size-fits-all model. "For mostly every couple I have seen, it"s hard to see how they got together in the first place," she says. "So unless you really get to know the nuanced dynamics, you will never "get it" or be able to help." Christine Fasano was married for only 14 months before getting a divorce last year. She agrees the dynamics of a relationship are nuanced and complex—but also sees merit in the University of Washington study"s basic assumption that if one looks starkly at interaction between a couple, it is possible to ascertain whether the relationship is headed toward demise. "I"m not surprised the model works," she says. "It"s actually not that profound. My basic observation of couples that are happily married is that they treat each other well. That is basically what they are saying, and that is hard to argue with." So, any final advice for Valentine"s Day from the divorce research team out in Washington? "I would never give advice on matters of the heart," says Murray, who, incidentally, has been married 45 years. "But I suppose the bottom line is, yes, communication. And being good to one another. That is nice to quantify."

单选题 We have all heard of counterfeiting before. Usually it refers to people making money— printing it instead of earning it. But counterfeiting also can involve all sorts of consumer goods and manufactured products. From well-known brand names such as Calvin Klein jeans to auto parts, counterfeiters have found ways to produce goods that look authentic. In some instances, counterfeit products look better than the original! The demand of brand-name products has helped counterfeiting grow into a very profitable business throughout the world and into a serious problem for legitimate manufacturers and consumers alike. Faulty counterfeit parts have caused more than two dozen plane crashes. Most counterfeit auto parts do not meet federal safety standards. Counterfeiting hurts manufacturers in many ways. Analysts estimate that, in the United States alone, annual revenue lost runs from $6 billion to $8 billion perhaps even worse, consumers blame the innocent manufacturer when they unknowingly buy a counterfeit product and find it doesn't perform as expected. Sometimes entire economies can suffer. For instance, when farmers in Kenya and Zaire used counterfeit fertilizers, both countries lost most of their crops. In 1984 the U.S. government enacted the Trademark Counterfeiting Act and made counterfeiting of products a criminal offense punishable by fines and stiff jail terms. Unfortunately counterfeiting does not receive top priority from law enforcement officers and prosecutors. Legitimate firms therefore have the burden of finding their own raids and to fight the problem. IBM, with a court order, conducted its own raids and found' keyboards, displays, and boxes with its logo. The fake parts were used to create counterfeits of IBM's personal computer "XT". Some companies have developed secret product codes to identify the genuine article. They must change the codes periodically because counterfeiters learn the codes and duplicate them. Perhaps the most effective way for manufacturers to fight counterfeiting is to monitor the distribution network and make sure counterfeit products are not getting into the network. Some companies even hire investigators to track counterfeit products. By copying other firms' products, counterfeiters avoid research and development costs and most marketing costs. High-tech products such as computers and their software products are especially vulnerable. As long as counterfeiting is profitable, an abundance of products are available to copy, and the laws are difficult to enforce, counterfeiters can be expected to prosper for a long time.

单选题 Question 21-25 Species interdependence in nature confers many benefits on the species involved, but it can also become a point of weakness when one species involved in the relationship is affected by a catastrophe. Thus, flowering plant species dependent on insect pollination, as opposed to self- pollination or wind pollination, could be endangered when the population of insect-pollinators is depleted by the use of pesticides. In the forests of New Brunswick, for example, various pesticides have been sprayed in the past 25 years in efforts to control the spruce budworm, an economically significant pest. Scientists have now investigated the effects of the spraying of Matacil, one of the anti-budworm agents that is least toxic to insect-pollinators. They studied Matacil's effects on insect mortality in a wide variety of wild insect species and on plant fecundity, expressed as the percentage of the total flowers on an individual plant that actually developed fruit and bore seeds. They found that the most pronounced mortality after the spraying of Matacil occurred among the smaller bees and one family of flies, insects that were all important pollinators of numerous species of plants growing beneath the tree canopy of forests. The fecundity of plants in one common indigenous species, the red-osier dogwood, was significantly reduced in the sprayed areas as compared to that of plants in control plots where Matacil was not sprayed. This species is highly dependent on the insect-pollinators most vulnerable to Matacil. The creeping dogwood, a species similar to the red-osier dogwood, but which is pollinated by large bees, such as bumblebees, showed no significant decline in fecundity. Since large bees are not affected by the spraying of Matacil, these results add weight to the argument that spraying where the pollinators are sensitive to the pesticide used decreases plant fecundity. The question of whether the decrease in plant fecundity caused by the spraying of pesticides actually causes a decline in the overall population of flowering plant species still remains unanswered. Plant species dependent solely on seeds for survival or dispersal are obviously more vulnerable to any decrease in plant fecundity that occurs, whatever its cause. If, on the other hand, vegetative growth and dispersal (by means of shoots or runners) are available as alternative reproductive strategies for a species, then decreases in plant fecundity may be of little consequence. The fecundity effects described here are likely to have the most profound impact on plant species with all four of the following characteristics, a short life span, a narrow geographic range, an incapacity for vegetative propagation, and a dependence on a small number of insect- pollinator species. Perhaps we should give special attention to the conservation of such plant species since they lack key factors in their defenses against the environmental disruption caused by pesticide use.

单选题Questions 16 to 20 are based on the following talk.

单选题It can be inferred from the passage that the author considers Newcomb's comments more irresponsible than Comte's for which of the following reasons?

单选题 Nutritional statements that depend on observation or anecdote should be given serious consideration, but consideration should also be given to the physical and psychological quirks of the observer. The significance attached to an experimental conclusion depends, in part, on the scientific credentials of the experimentalist; similarly, the significance of selected observations depends, again in part, on the preconceptions of the observer. Regimes that are proposed by people who do not look as if they enjoyed their food, and who do not themselves have a well-fed air, may not be ideal for normal people. Graham Lusk, who combined expert knowledge with a normal appreciation of good food, describes how he and Chittenden, who advocated a low-protein diet, spent some weeks in Britain eating the rations of the 1914-1918 war and then got more ample rations on board ship. Lusk attributed his sense of well-being to the extra meat he was eating; Chittenden attributed it to the sea air. When young animals are reared for sale as meat, the desirable amount of protein in their food is a simple matter of economics. Protein is expensive, so the amount given is increased up to the level at which the increased rate of growth is offset by the increased cost of the diet. As already mentioned, the efficiency with which protein is used to build the body diminishes as the percentage of protein in the diet increases. In practice, the best diets seem to contain between 15 and 25 per cent protein. It is not certain that maximum growth rate is desirable in children; some experiments with rats suggest that rapid growth is associated with a shorter ultimate expectation of life. There are practical and ethical obstacles to human experiments in which the effect of protein can be measured. Children do not grow as fast as the young animals in which there is a commercial interest. Their need for protein is therefore presumably smaller, but there is no evidence that the desirable protein level, after weaning, is less than 15 per cent. An argument against this percentage of protein is that in human milk only 13 per cent of the solid material is protein. That protein is, however, of better quality than any protein likely to be given to infants that are not weaned on cow's milk. Furthermore, milk, like other products of evolution, is a compromise. Mothers are not expendable. A species would not long survive if mothers depleted their own proteins so much in the course of feeding the first child that the prospects of later children were seriously jeopardized. Human milk is no doubt a good food, but the assumption that it is necessarily ideal is stretching belief in the beneficence and perfection of Nature too far.

单选题Questions 11～14

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