单选题The______to the contract must be signed by two witnesses.

单选题Also of concern was the fact that many consumers lacked sufficient information and awareness to protect themselves in the marketplace and to make knowledgeable buying choices.

单选题Rebecca ______ home, for I saw her just now at the canteen. A. mustn't have gone B. shouldn't have gone C. can't have gone D. couldn't have gone

单选题The wagon trains had to______Indian territory to reach California.

单选题If the man is only interested in your appearance, ______ just shows how shallow he is.

单选题When we feel stressed, our adrenal glands release a peptide called Cortisol. Our body responds with Cortisol whether it faces physical, environmental, academic, or emotional danger. This triggers a string of physical reactions including depression of the immune system, tensing of the large muscles, blood-clotting, and increasing blood pressure. It's the perfect response to the unexpected presence of a sable-toothed tiger. But in school, that kind of response leads to problems. Chronically high Cortisol levels lead to the death of brain cells in the hippocampus, which is critical to explicit memory formation. These physical changes are significant. Stanford scientist Robert Sapolsky found that atrophy levels in the hippocampus of Vietnam veterans with PTSD (post-traumatic stress disorder) ranged from 8 to 24 percent above the control group. Chronic stress also impairs a student's ability to sort out what's important and what's not. Jacobs and Nadel (1985) suggest that thinking and memory are affected under stress. The brain's short-term memory and ability to form long-term memories are inhibited. There are other problems. Chronic stress makes students more susceptible to illness. In one study, students showed a depressed immune system at test time; they had lower levels of an important antibody for fighting infection. This may explain the vicious academic cycle; more test stress means more sickness, which means poor health and missed classes, which contribute to lower test scores. A stressful physical environment is linked to student failure. Crowded conditions, poor student relationships, and even lighting can matter. Optometrist Ray Gottlieb says that school stress causes vision problems. That in turn impairs academic achievement and self-esteem. He says that, typically, a stressed child will constrict breathing and change how he or she focuses to adapt to the stress. This pattern hurts learning in the short and long run. Under stress, the eyes become more attentive to peripheral areas as a natural way to spot predators first. This makes it nearly impossible to track across a page of print, staying focused on small areas of print.

单选题In Paris a record 81 international designers unveiled spring/summer collections, which resulted in fashion confusion.

单选题Fluoride deters tooth decay by reducing the growth of bacteria that destroy tooth enamel.

单选题On August 18th the president announced a general______for political exiles.

单选题—When were your legs injured?—It was on a Sunday last month______my father and I spent our holiday at the seaside.

单选题David Landes, author of The Wealth and Poverty of Nations: Why Some Are So Rich and Some So Poor , credits the world"s economic and social progress over the last thousand years to "Western civilization and its dissemination". The reason, he believes, is that Europeans invented systematic economic development. Landes adds that three unique aspects of culture were crucial ingredients in Europe"s economic growth. First, science developed as an autonomous method of intellectual inquiry that successfully disengaged itself from the social constraints of organized religion and from the political constraints of centralized authority. Though Europe lacked a political center, its scholars benefited from the use of a single vehicle of communication: Latin. This common tongue facilitated an adversarial discourse in which new ideas about the physical world could be tested, demonstrated, and then accepted across the continent and eventually across the world. Second, Landes espouses a generalized form of Max Weber"s thesis that the values of work, initiative, and investment made the difference for Europe. Despite his emphasis on science, Landes does not stress the notion of rationality as such. In his view, "what counts is work, thrift, honesty, patience, and tenacity." The only route to economic success for individuals or states is working hard, spending less than you earn, and investing the rest in productive capacity. This is his fundamental explanation of the problem posed by his book"s subtitle: "Why Some Are So Rich and Some So Poor". For historical reasons—an emphasis on private property, an experience of political pluralism, a temperate climate, an urban style—Europeans have, on balance, followed those practices and therefore have prospered. Third, and perhaps most important, Europeans were learners. They "learned rather greedily", as Joel Mokyr put it in a review of Landes"s book. Even if Europeans possessed indigenous technologies that gave them an advantage (spectacles, for example), as Landes believes they did, their most vital asset was the ability to assimilate knowledge from around the world and put it to use—as in borrowing the concept of zero and rediscovering Aristotle"s Logic from the Arabs and taking paper and gunpowder from the Chinese via the Muslim world. Landes argues that a systematic resistance to learning from other cultures had become the greatest handicap of the Chinese by the eighteenth century and remains the greatest handicap of Arab countries today. Although his analysis of European expansion is almost nonexistent, Landes does not argue that Europeans were beneficent bearers of civilization to a benighted world. Rather he relies on his own commonsense law: "When one group is strong enough to push another around and stands to gain by it, it will do so." In contrast to the new school of world historians, Landes believes that specific cultural values enabled technological advances that in turn made some Europeans strong enough to dominate people in other parts of the world. Europeans therefore proceeded to do so with great viciousness and cruelty. By focusing on their victimization in this process, Landes holds, some postcolonial states have wasted energy that could have been put into productive work and investment, if one could sum up Landes"s advice to these states in one sentence, it might be "Stop whining and get to work." This is particularly important, indeed hopeful, advice, he would agree, because success is not permanent. Advantages are not fixed, gains from trade are equal, and different societies react differently to market signals. Therefore, not only is there hope for undeveloped countries, but developed countries have little cause to be complacent, because the current situation "will press hard" on them. The thrust of studies like Landes"s is to identify those distinctive features of European civilization that lie behind Europe"s rise to power and the creation of modernity more generally. Other historians have placed a greater emphasis on such features as liberty, individualism, and Christianity. In a review essay, the art historian Craig Clunas listed some of the less well known linkages that have been proposed between Western culture and modernity, including the propensities to think quantitatively, enjoy pornography, and consume sugar. All such proposals assume the fundamental aptness of the question: What elements of European civilization led to European success? It is a short leap from this assumption to outfight triumphalism. The paradigmatic book of this school is, of course, The End of History and the Last Man , in which Francis Fukuyarna argues that after the collapse of Nazism in the twentieth century, the only remaining model for human organization in the industrial and communications ages is a combination of market economics and limited, pluralist, democratic government.

单选题Cellular slime molds are extraordinary life forms that exhibit features of both fungi and protozoa, although often classed for convenience with fungi. At one time they were regarded as organisms of ambiguous taxonomic status, but more recent analysis of DNA sequences has shown that slime molds should be regarded as inhabiting their own separate kingdom. Their uniqueness lies in their unusual life cycle, which alternates between a feeding stage in which the organism is essentially unicellular and a reproductive stage in which the organism adopts a multicellular structure. At the first stage they are free-living, separate amoebae, usually inhabiting the forest floor and ingesting bacteria found in rotting wood, dung, or damp soil. But their food supplies are relatively easily exhausted since the cells' movements are restricted and their food requirements rather large. When the cells become starved of nutrition, the organism initiates a new genetic program that permits the cells to eventually find a new, food-rich environment. At this point, the single-celled amoebae combine together to form what will eventually become a multicellular creature. The mechanism by which the individual members become a single entity is essentially chemical in nature. At first, a few of the amoebae start to produce periodic chemical pulses that are detected, amplified, and relayed to the surrounding members, which then move toward the pulse origin. In time, these cells form many streams of cells, which then come together to form a single hemispherical mass. This mass sticks together through the secretion of adhesion molecules. The mass now develops a tip, which elongates into a finger-like structure of about 1 or 2 millimeters in length. This structure eventually falls over to form a miniature slug, moving as a single entity orienting itself toward light. During this period the cells within the mass differentiate into two distinct kinds of cell. Some become prestalk cells, which later form into a vertical stalk, and others form prespore cells, which become the spore head. As the organism migrates, it leaves behind a track of slime rather like a garden slug. Once a favorable location has been found with a fresh source of bacteria to feed on, the migration stops and the colony metamorphoses into a fungus-like organism in a process known as "culmination." The front cells turn into a stalk, and the back cells climb up the stalk and form a spherical-shaped head, known as the sorocarp. This final fruiting body is about 2 millimeters in height. The head develops into spores, which are dispersed into the environment and form the next generation of amoebae cells. Then the life cycle is repeated. Usually the stalk disappears once the spores have been released. The process by which the originally identical cells of the slime mold become transformed into multicellular structures composed of two different cell types — spore and stalk — is of great interest to developmental biologists since it is analogous to an important process found in higher organisms in which organs with highly specialized functions are formed from unspecialized stem cells. Early experiments showed which parts of the slime mold organism contributed to the eventual stalk and which parts to the head. Scientists stained the front part of a slug with a red dye and attached it to the back part of a different slug. The hybrid creature developed as normal. The experimenters then noted that the stalk of the fruiting body was stained red and that the spore head was unstained. Clearly, the anterior part of the organism culminated in the stalk and the posterior part in the spore head. Nowadays, experiments using DNA technology and fluorescent proteins or enzymes to label the prespore and prestalk cells have been undertaken. This more molecular approach gives more precise results than using staining dyes but has essentially backed up the results of the earlier dye studies.

单选题______ the door when a gust of wind blew the candle out.

单选题The police caught the thief on the street and______him into their van.

单选题When we eat may be just as important as what we eat. A new study shows that mice that eat when they should be sleeping gain more weight than mice that eat at normal hours. Another study sheds light on why we pack on the pounds in the first place. Whether these studies translate into therapies that help humans beat obesity remains to be seen, but they give scientists clues about the myriad factors that they must take into account. Observations of overnight workers have shown that eating at night disrupts metabolism and the hormones that signal we"re sated. But no one had done controlled studies on this connection until now. Biologist Fred Turek of Northwestern University in Evanston, Illinois, and graduate student Deanna Arble examined the link between a high-fat diet and what time of day mice eat. A control group of six nocturnal mice ate their pellets (60% fat by calories, mostly lard) during the night. Another group of six ate the same meal during the day, Turek says, which disrupts their circadian rhythm—the body"s normal 24-hour cycle. After 6 weeks, the off-schedule mice weighed almost 20% more than the controls, Turek and Arble report today in Obesity, supporting the idea that consuming calories when you should be sleeping is harmful. Turek and Arble acknowledge that the disrupted mice ate a tad more and were a tad more sluggish, but the differences could not account for all of the weight gain. In the second study, a different team of researchers investigated the link between weight and the immune system. Hundreds of genes seem to affect the accumulation of fat, but one that helps protect us from infection might help us lose weight with little effort, biochemist Alan Saltiel of the University of Michigan, Ann Arbor, and colleagues suggest today in Cell. The researchers tested me weight-adding abilities of a protein called IKK ∈ , which is linked with obesity, diabetes, and chronic, low-level inflammation. For 3 months, the team fed six mice missing IKK ∈ genes a diet of high-fat chow. Because IKKE"s main job is immune defense, Saltiel"s team didn"t expect to find weight differences between knockout mice and controls. But the knockout mice did gain significantly less. Best of all, the girth the animals did add was less harmful to their overall health. "The knockout mice don"t gain as much weight but also don"t get diabetes, don"t get insulin resistance, and don"t get accumulation of lipids on the liver," Saltiel says, all of which contribute to the suite of health problems associated with being overweight. Saltiel calls IKK e " an especially appealing drug target for the treatment of metabolic disease. " Tom Maniatis, a molecular biologist at Harvard University praises the study but remains skeptical about any drug that would inhibit IKK ∈ . He helped develop the mice used in the experiment and notes that they are vulnerable to the flu. He suspects that suppressing IKK ∈ may help people with diabetes or obesity, "but the first time the swine flu comes along, that"s it. Researchers are also enthusiastic about the circadian rhythm paper Frank Scheet, a neuroscientist at Harvard who studies sleep, was struck that " you could see something happening [ to the disrupted mice] in the first week already. That"s consistent with human studies where we found changes in just 3 days. " Together, the papers suggest that there"s no simple answer to why people gain weight. Says Turek, "It"s clearly not just calories in versus calories out. "

单选题The committee has anticipated the problems that ______ in the road construction project. A. arise B. will arise C. arose D. have arisen

单选题The spellings of many Old English words have been ______ in the living language, although their pronunciations have changed.

单选题My company is House Furnishing Corporation, there is a ready market for kitchenware in our area.

单选题The ______family in Chinese cities now spends more money on housing than before.

单选题The______workroom has not been used in years.