单选题The reason for their unusual behavior remains a puzzle .

单选题Dangers Await Babies with Altitude Women who live in the world's highest communities tend to give birth to under-weight babies, a new study suggests. These babies may grow into adults with a high risk of heart disease and strokes. Research has hinted that newborns in mountain communities are lighter than average. Bur it wasn't clear whether this is due to reduced oxygen levels at high altitude or because their mothers are under-nourished — many people who live at high altitudes are relatively poor compared with those living lower down. To find out more, Dino Giussani and his team at Cambridge University studied the records of 400 births in Bolivia during 1997 and 1998. The babies were born in both rich and poor areas of two cities: La Paz and Santa Cruz. La Paz is the highest city in the world, at 3.65 kilometers above sea level, while Santa Cruz is much lower, at 0.44 kilometers. Sure enough, Giussani found that the average birthweight of babies in La Paz was significantly lower than in Santa Cruz. This was true in both high and low-income families. Even babies born to poor families in Santa Cruz were heavier on average than babies born to wealthy families in lofty La Paz. "We were very surprised by this result, " says Giussani. The results suggest that babies born at high altitude are deprived of oxygen before birth. "This may trigger the release or suppression of hormones that regulate growth of the unborn child. " says Giussani. His team also found that high-altitude babies tended to have relatively larger heads compared with their bodies. This is probably because a fetus starved of oxygen will send oxygenated blood to the brain in preference to the rest of the body. Giussani wants to find out if such babies have a higher risk of disease in later life. People born in La Paz might be prone to heart trouble in adulthood, for example. Low birthweight is a risk factor for coronary heart disease. And newborns with a high ratio of head size to body weight are often predisposed to high blood pressure and strokes in later life.

单选题I don't know why everything around me is going into confusion.A. considerationB. puzzleC. attractionD. contradiction

单选题The river widens considerably as it begins to turn west.

单选题 下面有3篇短文，每篇短文后有5道题，每题后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题，从4个选项中选择1个最佳答案。{{B}}第一篇{{/B}} {{B}} Diseases of Agricultural Plants{{/B}} Plants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack com, and about as many attack wheat. The results of unchecked plant disease are all too obvious in countries which have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries which are now amply fed by their agricultural products there could soon be critical food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world. Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. The tolerance of a particular plant changes as the growing conditions change. A blight may be but a local infection easily controlled; on the other hand it can attack particular plants in a whole region or nation. An example is the blight which killed virtually every chestnut tree in North America. Another is the famous potato blight in Ireland in the last century. As a result of that, it was estimated that one million people died of starvation and related ailments. Plant pathologists have made remarkable strides in identifying the pathogens of the various diseases. Bacteria may invade a plant through an infestation of insect parasites carrying the pathogen. A plant can also be inoculated by man. Other diseases might be caused by fungus which attacks the plant in the form of a mold or smut or rust. Frequently such a primary infection8 will weaken the plant so that a secondary infection may result from9 its lack of tolerance. The symptoms shown may cause an error in diagnosis, so that treatment may be directed toward bacteria which could be the result of a susceptibility caused by a primary virus infection.

单选题Because of its vivid yellow, black and orange coloring, the emperor penguin stands out against the usually bleak landscape of its habitat.A. oddB. paleC. brightD. simple

单选题Pool Watch Swimmers can drown in busy swimming pools when lifeguards fail to notice that they are in trouble. The Royal Society for the Prevention of Accidents says that on average 15 people drown in British pools each year, but many more suffer major injury after getting into difficulties. Now a French company has developed an artificial intelligence system called Poseidon that sounds the alarm when it sees someone in danger of drowning. When a swimmer sinks towards the bottom of the pool, the new system sends an alarm signal to a poolside monitoring station and a lifeguard"s pager. In trials at a pool in Ancenis, near Nantes, it saved a life within just a few months, says Alistair McQuade, a spokesman for its maker, Poseidon Technologies. Poseidon keeps watching through a network of underwater and overheard video cameras. AI software analyses the images to work out swimmers" trajectories. To do this reliably, it has to tell the difference between a swimmer and the shadow of someone being cast onto the bottom or side of the pool. "The underwater environment is a very dynamic one, with many shadows and reflections dancing around," says McQuade. The software does this by "projecting" a shape in its field of view onto an image of the far wall of the pool. It does the same with an image from another camera viewing the shape from a different angle. If the two projections are in the same position, the shape is identified as a shadow and is ignored. But if they are different, the shape is a swimmer and so the system follows its trajectory. To pick out potential drowning victims, anyone in the water who starts to descend slowly is added to the software"s "pre-alert" list, says McQuade. Swimmers who then stay immobile on the pool bottom for 5 seconds or more are considered in danger of drowning. Poseidon double-checks that the image really is of a swimmer, not a shadow, by seeing whether it obscures the pool"s floor texture when viewed from overhead. If so, it alerts the lifeguard, showing the swimmer"s location on a poolside screen. The first full-scale Poseidon system will be officially opened next week at a pool in High Wycombe, Buckinghamshire. One man who is impressed with the idea is Travor Baylis, inventor of the clockwork radio. Baylis runs a company that installs swimming pools, and he was once an underwater escapologist with a circus. "I say full marks to them if this works and can save lives," he says. But he adds that any local authority spending ￡30,000 plus on a Poseidon system ought to be investing similar amounts in teaching children to swim.

单选题He could not tolerate the extremes of heat in the desert.

单选题You'd better have the dog {{U}}surveyed {{/U}}before you offer to buy it.

单选题If wool is put into hot water, it tends to {{U}}shrink{{/U}}. A. disappear B. expand C. break D. contract

单选题Hillman's study, which will be published later this year, isn't definitive enough to stand alone. But it doesn't have to: it's part of a recent and rapidly growing movement in science showing that exercise can make people smarter. Last week, in a landmark paper, researchers announced that they had coaxed (耐心谨慎地摆弄) the human brain into growing new nerve cells, a process that for decades had been thought impossible, simply by putting subjects on a three -month aerobic - workout regimen (养生之道). Other scientists have found that vigorous exercise can cause older nerve cells to form dense, interconnected webs that make the brain run faster and more efficiently. And there are clues that physical activity can stave off the beginnings of Alzheimer's disease, ADHD and other cognitive disorders. No matter your age, it seems, a strong, active body is crucial for building a strong, active mind. What is the main idea of the paragraph?A. Exercising can cause a chain of chemical reactions in the brain.B. Exercising is helpful building a strong, active mind.C. Exercising is a good way to keep fit and stay healthy.D. Exercising can help the brain grow new nerve cells.

单选题Companies whose profits do not exceed $ 1500 in any one year may opt to pay income tax at the rate of 20%.A. chooseB. operateC. manageD. decide

单选题In the first decades of this century, the individual gene could be worked with fruitfully.A. blindlyB. completelyC. productivelyD. carefully

单选题 First Self Contained Heart Implanted A patient on the brink of death has received the world's first self-contained artificial heart—a battery powered device about the size of a softball that runs without the need for wires, tubes or hoses sticking out of the chest. Two surgeons from the University of Louisville implanted the titanium and plastic pump during a seven-hour operation at Jewish Hospital Monday. The hospital said the patient was "awake and responsive" Tuesday and resting comfortably. It refused to release personal details. The patient had been expected to die within a month without the operation, and doctors said they expected the artificial heart to extend the person's life by only a month. But the device is considered a major step toward improving the patient's quality of life. The new pump, called AbioCor, is also a technological leap from the mechanical hearts used in the 1980s, which were attached by wires and tubes to bulky machinery outside the body. The most famous of those, the Jarvic-7, used air as a pumping device and was attached to an apparatus about the size of a washing machine. "I think it's potentially a major step forward in the artificial heart development," said Dr. David Faxon, president of the American Heart Association. However, he said the dream of an implantable, permanent artificial heart is not yet a reality. "This is obviously an experimental device whose long-term success has to be demonstrated." Only about half of the 4,200 Americans on a waiting list for donor hearts received them last year, and most of the rest died. Some doctors, including Robert Higgins, chairman of cardiology at the Medical College of Virginia in Richmond, said artificial hearts are unlikely to replace donor hearts. "A donor heart in a good transplant can last 15 to 30 years," he said. "It's going to be hard to replace that with a machine." The AbilCor has a 2-pound pumping unit, and electronic controls that adjust the pumping speed based on the body's needs. It is powered by a small battery pack worn outside the body that transmits current through the skin.

单选题New Foods and the New World In the last 500 years, nothing about people-not their clothes, ideas, or languages-has changed as much as what they eat. The original chocolate drink was made from the seeds of the cocoa tree by South American Indians. The Spanish introduced it to the rest of the world during the 1500's. And although it was very expensive, it quickly became fashionable. In London shops where chocolate drinks were served became important meeting places. Some still exist today. The potato is also from the New World. Around 1600, the Spanish brought it from Peru to Europe, where it soon was widely grown. Ireland became so dependent on it that thousands of Irish people starved when the crop failed during the "Potato Famine" of 1845-1846, and thousands more were forced to emigrate to America. There are many other foods that have traveled from south America to the Old World. But some others went in the opposite direction. Brazil is now the world's largest grower of coffee, and coffee is an important crop in Colombia and other South American countries. But it is native to Ethiopia. It was first made into a drink by Arabs during the 1400's. According to an Arabic legend, coffee was discovered when a goatherd named Kaldi noticed that his goats were attracted to the red berries on a coffee bush. He tried one and experienced the "wide-awake" feeling that one-third of the world's population now starts the day with.

单选题{{B}}第三篇{{/B}} Why does cream go bad faster than butter? Some researchers think they have the answer, and it comes down to the structure of the food, not its chemical composition--a finding that could help rid some processed foods of chemical preservatives. Cream and butter contain pretty much the same substances, so why cream should sour much faster has been a mystery. Both are emulsions--tiny globules(小球体)of one liquid evenly distributed throughout another. The difference lies in what's in the globules and what's in the surrounding liquid, says Brocklehurst, who led the investigation. In cream, fatty globules drift about in a sea of water. In butter, globules of a watery solution are locked away in a sea of fat. The bacteria which make the food go bad prefer to live in the watery regions of the mixture. "This means that in cream, the bacteria are free to grow throughout the mixture," he says. When the situation is reversed, the bacteria are locked away in compartments(隔仓室)buried deep in the sea of fat. Trapped in this way, individual colonies cannot spread and rapidly run out nutrients(养料). They also slowly poison themselves with their waste products. "In butter, you get a self--limiting system which stops the bacteria growing," says Broeklehurst. The researchers are already working with food companies keen to see if their products can be made resistant to bacterial attack through alterations to the food's structure. Brocklehurst believes it will be possible to make the emulsions used in salad cream, for instance, more like that in butter. The key will be to do this while keeping the salad cream liquid and not turning in into a solid lump.

单选题In the United States,the national flag is usually displayed outdoor between sunrise and sunset.

单选题Patricia stared at the other girls with resentment .

单选题I didn't ask because I was afraid of looking Ustupid/U.

单选题Below 600 feet ocean waters range from dimly lit to completely dark. A. inadequately B. hardly C. faintly D. sufficiently