单选题They demanded that the government __________ all political prisoners in the next two days.

单选题She ought to stop work; she has a headache because she ______ too long. A. has been reading B. had read C. is reading D. read

单选题They bought the land with a ______ to build a new office block.

单选题It is necessary that a person ______ exercises every day if he wishes to be healthy.

单选题The main concern of the last paragraph is______.

单选题He learned how to use sign language to______with deaf customers.

单选题Scientists have been struggling to find out the reason behind blushing （脸红）。Why would humans evolve（进化） a ____请作答此空______ that puts us at a social disadvantage by 22__________ us to reveal that we hav

单选题Neither of us ______ to undertake the responsibility.

单选题Is it more ______ to buy a large box of candy than two small boxes?

单选题 在中国，玉(jade)的历史可以追溯到商朝(the Shang Dynasty)。数千年来，人们都视玉为最珍贵的石头。在古代，玉是仅限于宗教仪式的物品。在封建社会(imperial society)，玉是财富和社会地位的象征。人们普遍相信玉能辟邪，能保护佩戴者免于灾祸。玉饰不仅能使佩戴者更美丽，还能促进其身体健康。中国的玉石种类有很多，其中最出名的是新疆的和田玉。

单选题Many critics of the current welfare system argue that existing welfare regulations foster family instability. They maintain that those regulations, which exclude most poor husband and wife families from Aid to Families with Dependent Children assistance grants, contribute to the problem of family dissolution. Thus, they conclude that expanding the set of families eligible for family assistance plans or guaranteed income measures would result in a marked strengthening of the low-income family structure. If all poor families could receive welfare, would the incidence of instability change markedly? The unhappily married couple, in most cases, remain together out of a sense of economic responsibility for their children, because of the high costs of separation, or because of the consumption benefits of marriage. The formation, maintenance, and dissolution of the family is in large part a function of the relative balance between the benefits and costs of marriage as seen by the individual members of the marriage. The major benefit generated by the creation of a family is the expansion of the set of consumption possibilities. The benefits from such a partnership depend largely on the relative dissimilarity of the resources or basic endowments each partner brings to the marriage. Persons with similar productive capacities have less economic "cement" holding their marriage together. Since the family performs certain function society regards as vital, a complex network of social and legal buttresses has evolved to reinforce marriage. Much of the variation in marital stability across income classes can be explained by the variation in costs of dissolution imposed by society, e. g. division of property, alimony, child support, and the social stigma attached to divorce. Marital stability is related to the costs of achieving an acceptable agreement on family consumption and production and to the prevailing social price of instability in the marriage partners social economic group. Expected AFDC income exerts pressures on family instability by reducing the cost of dissolution. To the extent that welfare is a form of government subsidized alimony payments, it reduces the institutional costs of separation and guarantees a minimal standard of living for wife and children. So welfare opportunities are a significant determinant of family instability in poor neighborhoods, but this is not the result of AFDC regulations that exclude most intact families from coverage. Rather, welfare instability occurs because public assistance lowers both the benefits of marriage and the costs of its disruption by providing a system of government subsidized alimony payments.

单选题You ______ me your telephone number in case someone wants to contact you.

单选题The prices of fridges have been ______ recently.

单选题Five cloned piglets, genetically modified so that their organs are much less likely to be rejected by a human donor recipient, have been born in the US. More than 62000 people in the US alone are waiting to receive donated hearts, lungs, livers, kidneys and pancreases. The number of human donors falls far short of demand. Pig organs are of a similar size to human organs, and some scientists hope they might be used to help meet the shortfall. But previous attempts to transplant unaltered pig tissue into humans have failed, due to immune rejection of the tissue. The five piglets, born on Christmas Day, lack a gene for an enzyme that adds a sugar to the surface of pig ceils. The sugar would trigger a patient's immune system into launching an immediate attack. "This advance provides a near-time solution for overcoming the shortage of human organs for transplants, as well as insulin-producing cells to cure diabetes," says David Ayares, vice president of research at PPL Therapeutics, US division, where the pigs were created. "This is the key gene for overcoming the early stage of rejection. " However, scientists warn that much more work is necessary before organs from copies of the pigs could be transplanted into humans. Human genes will need to be added, to prevent rejection of the organ in the long-term. There are also concerns that pig viruses could infect organ recipients. Cloning techniques were vital to the production of the pigs. Genes can only be knocked out in a single cell. Cloning of these single cells then allowed the creation of a whole animal in which the gene was knocked out in every cell. But the PPL researchers have succeeded in knocking out only one copy of the gene for the enzyme, called alpha 1, 3 galactosyl transferase, The team will now attempt to knock out both copies of the gene. "There will also be other genes we will incorporate into our program," Ayares says. "We don't think that one gene is going to produce an organ that's going to be the end-all for transplantation. We're going to have to add two to three human genes as well. " The team will also conduct tests to investigate whether so-called porcine endogenous retroviruses (PERVS) from the pigs could infect human cells in culture. But Ayares hopes that organs created from PPL pigs could be transplanted into patients within five years. "But although a lot of the stem cell work is very exciting, we're still very far off being able to grow an organ in a culture dish," says Julia Greenstein of Immerge Bio Therapeutics in Charlestown, US, who is working on creating similar knock-out pigs with researchers at the University of Missouri.

单选题I cannot sleep. The dog next door is making too much noise. I wish it ______ quiet.

单选题 Does the Internet Make You Dumber? A. The Roma- philosopher Seneca may have put it best 2000 years ago: 'To be everywhere is to be nowhere.' Today, the Internet grants us easy access to unprecedented amounts of information. But a growing body of scientific evidence suggests that the Net, with its constant distractions and interruptions, is also turning us into disrupted and superficial thinkers. B. The picture emerging from the research is deeply troubling, at least to anyone who values the depth, rather than just the velocity (速度), of human thought. People who read text studded with links, the studies show, comprehend less than those who read traditional linear text. People who watch busy multimedia presentations remember less than those who take in information in a more sedate (镇定的) and focused manner. People who are continually distracted by e-mails, alerts and other messages understand less than those who are able to concentrate. And people who juggle (同时应会) many tasks are less creative and less productive than those who do one thing at a time. C. The common thread in these disabilities is dispersing our attention. The richness of our thoughts, our memories and even our personalities hinges on our ability to focus the mind and sustain concentration. Only when we pay deep attention to a new piece of information are we able to associate it 'meaningfully and systematically with knowledge already well established in memory,' writes the Nobel Prize winning neuroscientist (神经科学家) Eric Kandel. Such associations are essential to mastering complex concepts. D. When we're constantly distracted and interrupted, as we tend to be online, our brains are unable to generalize the strong and expansive neural connections that give depth and distinctiveness to our contemplating. We become mere signal-processing units, quickly shepherding disjointed bits of information into and then out of short-term memory. E. In an article published in Science last year, Patricia Greenfield, a leading developmental psychologist, reviewed dozens of studies on how different media technologies influence our cognitive abilities. Some of the studies indicated that certain computer tasks, like playing video games, can enhance 'visual literacy skills', increasing the speed at which people can shift their focus among icons and other images on screens. Other studies, however, found that such rapid shifts in focus, even if performed adeptly, result in less rigorous and 'more automatic' thinking. F. In one experiment conducted at Cornell University, for example, half a class of students was allowed to use Internet-connected laptops during a lecture, while the other had to keep their computers shut. Those who browsed the Web performed much worse on a subsequent test of how well they retained the lecture's content. While it's hardly surprising that Web surfing would distract students, it should be a note of caution to schools that are wiring their classrooms in hopes of improving learning. G. Ms. Greenfield concluded that 'every medium develops some cognitive skills at the expense of others.' Our growing use of screen-based media, she said, has strengthened visual-spatial intelligence, which can improve the ability to do jobs that involve keeping track of lots of simultaneous signals, like air traffic control. But that has been accompanied by 'new weaknesses in higher-order cognitive processes,' including 'abstract vocabulary, mindfulness, reflection, inductive problem solving, critical thinking, and imagination'. We're becoming, in a word, shallower. H. In another experiment, recently conducted at Stanford University's Communication between Humans and Interactive Media Lab, a team of researchers gave various cognitive tests to 49 people who do a lot of media multitasking and 52 people who multitask much less frequently. The heavy multitaskers performed poorly on all the tests. They were more easily distracted, had less control over their attention, and were much less able to distinguish important information from trivial. I. The researchers were surprised by the results. They had expected that the intensive multitaskers would have gained some unique mental advantages from all their on-screen juggling. But that wasn't the case. In fact, the heavy multitaskers weren't even good at multitasking. They were considerably less adept at switching between tasks than the more infrequent multitaskers. 'Everything distracts them,' observed Clifford Nass, the professor who heads the Stanford lab. J. It would be one thing if the ill effects went away as soon as we turned off our computers and cellphones. But they don't. The cellular structure of the human brain, scientists have discovered, adapts readily to the tools we use, including those for finding, storing and sharing information. By changing our habits of mind, each new technology strengthens certain neural pathways and weakens others. The cellular alterations continue to shape the way we think even when we're not using the technology. K. The pioneering neuroscientist Michael Merzenich believes our brains are being 'massively remodeled' by our ever-intensifying use of the Web and related media. In the 1970s and 1980s, Mr. Merzenich, now a professor emeritus at the University of California in San Francisco, conducted a famous series of experiments on primate brains that revealed how extensively and quickly neural circuits change in response to experience. When, for example, Mr. Merzenich rearranged the nerves in a monkey's hand, the nerve cells in the animal's sensory cortex quickly reorganized themselves to create a new 'mental map' of the hand. In a conversation late last year, he said that he was profoundly worried about the cognitive consequences of the constant distractions and interruptions the Internet bombards us with. The long-term effect on the quality of our intellectual lives, he said, could be 'deadly'. L. What we seem to be sacrificing in all our surfing and searching is our capacity to engage in the quieter, attentive modes of thought that underpin contemplation, reflection and introspection. The Web never encourages us to slow down. It keeps us in a state of perpetual mental locomotion. It is revealing, and distressing, to compare the cognitive effects of the Internet with those of an earlier information technology, the printed book. Whereas the Internet scatters our attention, the book focuses it. Unlike the screen, the page promotes contemplativeness. M. Reading a long sequence of pages helps us develop a rare kind of mental discipline. The innate bias of the human brain, after all, is to be distracted. Our predisposition is to be aware of as much of what's going on around us as possible. Our fast-paced, reflexive shifts in focus were once crucial to our survival. They reduced the odds that a predator would take us by surprise or that we'd overlook a nearby source of food. N. To read a book is to practice an unnatural process of thought. It requires us to place ourselves at what T.S. Eliot, in his poem 'Four Quartets', called 'the still point of the turning world'. We have to forge or strengthen the neural links needed to counter our instinctive distractedness, thereby gaining greater control over our attention and our mind. O. It is this control, this mental discipline, which we are at risk of losing as we spend ever more time scanning and skimming online. If the slow progression of words across printed pages damped our craving to be inundated by mental stimulation, the Internet indulges it. It returns us to our native state of distractedness, while presenting us with far more distractions than our ancestors ever had to contend with.—Nicholas Carr is the author, most recently, of The Shallows. What the Internet Is Doing to Our Brains.

单选题Cars and motorcycles are similar ______ they are both privately owned means of transport.

单选题A: My apartment is only 10 minutes' walk from the office. Why don't you drop by some time?B: ______. A. Because I didn't know you live so close by. B. Because I didn't want to bother you. C. I'd love to. Can I take my roommate along? D. That's OK. I'll be there soon.

单选题Airplanes have made______.