题目内容
Wild ducks and other migratory (迁移的) birds could be important carriers of deadly bird flu, researchers say. Even so, the infectious-disease experts say there is no solid basis for killing wild birds to protect poultry and minimize the risk of human infection. The European team investigating the global spread of the H5N1 strain of avian influenza (禽流感) says certain duck species may be infecting wild bird populations. Geese and wading birds are also possible vectors (带菌者) of the virus, the team says. The team’s study was led by Bjorn Olsen of Umea University in Sweden. Olsen runs Europe’s largest wild-bird flu monitoring program. Studies have shown that influenza viruses in lake water, generally passed via bird feces(粪), can stay infectious for up to 30 days. The migration or feeding behavior of dabbling ducks could at least partially explain the spread of the H5N1 strain of bird flu, the researchers add. This group of duck species includes mallards, teal, pintails, and others that feed at or near the surface, where viruses in water are most likely to be picked up. Perhaps as a result, dabblers have the highest known rates of avian influenza infection, the study says. For instance, nearly 13 percent of mallards tested positive for bird flu. Other species tested include the American black duck (18.1 percent), blue-winged teal (11.5 percent), and northern pintail (11.2 percent). However, bird flu viruses appear to exist in ducks in a low-pathogenic form, meaning infection doesn’t usually lead to severe illness and death. "Dabbling ducks are for sure the prime hosts for low pathogenic viruses," said study co-author Ron Fouehier, a virologist at the Erasmus Medical Center in Rotterdam, Netherlands. "But the big question is, how much of our knowledge about these viruses can we translate to high-pathogenic viruses such as the H5NI strain of bird flu" In poultry avian viruses can mutate(变异) into more virulent influenza strains, including H5NI. If this mutated virus then finds its way back into wild populations, the birds could then spread the disease through migration. Some scientists have argued that wild birds infected with HN51 would be too ill to migrate. Swans, for instance, appear to be particularly vulnerable to the strain. "Swans apparently drop dead quite easily, but they are unlikely to be the vector because they are not going to fly very far if they are dead," Fouchier said. But the study team says that some birds that have been purposely infected for the sake of research show that wild birds can survive H5N1. "For some reason H5N1 has adapted so it no longer kills dabbling ducks," Fouchier said. This means the ducks may be able to spread the virus over a wide area. The study team says migratory geese may also be vectors, because they often graze in huge flocks, a practice that could encourage transmission. Migrating ducks, the researchers add, "could provide an intercontinental bridge" for bird flu to North America, which has not yet had any known cases of H5N1. According to the study team, ______ is a practice that can encourage transmission of the bird flu.
查看答案
搜索结果不匹配？点我反馈
更多问题
Clara came to Jordan’s. Some of the older hands, Fanny among them, remembered her earlier rule, and cordially disliked the memory. Clara had always been "ikey", reserved, and superior. She had never mixed with the girls as one of themselves. If she had occasion to find fault, she did it coolly and with perfect politeness, which the defaulter felt to be a bigger insult than crossness. Towards Fanny, the poor, over-strung hunchback, Clara was unfailingly compassionate and gentle, as a result of which Fanny shed more bitter tears than ever the rough tongues of the other overseers had caused her. There was something in Clara that Paul disliked, and much that piqued him. If she were about, he always watched her strong throat or her neck, upon which the blond hair grew low and fluffy. There was a fine down, almost invisible, upon the skin of her face and arms, and once he had perceived it, he saw it always. When he was at his work, painting in the afternoon, she would come and stand near him, perfectly motionless. Then he felt her, though she neither spoke nor touched him. Although she stood a yard away he felt as if he were in contact with her. Then he could paint no more. He flung down the brushes, and turned to talk to her. Sometimes she praised his work; sometimes she was critical and cold. "You are affected in that piece," she would say; and, as there was an element of truth in her condemnation, his blood boiled with anger. Again: "What of this" he would ask enthusiastically. "H’m!" She made a small doubtful sound. "It doesn’t interest me much." "Because you don’t understand it," he retorted. "Because I thought you would understand." She would shrug her shoulders in scorn of his work. She maddened him. He was furious. Then he abused her, and went into passionate exposition of his stuff. This amused and stimulated her. But she never owned that she had been wrong. During the ten years that she had belonged to the women’s movement she had acquired a fair amount of education, and, having had some of Miriam’s passion to be instructed, had taught herself French, and could read in that language with a struggle. She considered herself as a woman apart, and particularly apart, from her class. The girls in the spiral department were all of good homes. It was a small, special industry, and had a certain distinction. There was an air of refinement in both rooms. But Clara was aloof also from her fellow-workers. None of these things, however, did she reveal to Paul. She was not the one to give herself away. There was a sense of mystery about her. She was so reserved, he felt she had much to reserve. Her history was open on the surface, but its inner meaning was hidden from everybody. It was exciting. And then sometimes he caught her looking at him from under her brows with an almost furtive, sullen scrutiny, which made him move quickly. Often she met his eyes. But then her own were, as it were, covered over, revealing nothing. She gave him a little, lenient smile. She was to him extraordinarily provocative, because of the knowledge she seemed to possess, and gathered fruit of experience he could not attain. What Paul didn’t like in Clara was that
Questions 22 to 25 are based on the conversation you have just heard.
动脉血压升高可导（ ）
That Louise Johannes is believed by many critics to be the greatest twentieth-century sculptor is all the more remarkable because the greatest resistance to women artists has been, until recently, in the field of sculpture. Since Neolithic times, sculpture has been considered the prerogative of men, partly, perhaps, for purely physical reasons it was erroneously assumed that women were not suited for the hard manual labor required in sculpting stone, carving wood, or working in metal. It has been only during the twentieth century that women sculptors have been recognized as major artists, and it has been in the United States, especially since the decades of the fifties and sixties, that women sculptors have shown the greatest originality and creative power. Their rise to prominence parallels the development of sculpture itself in the United States, while there had been a few talented sculptors in the United States before the 1940’s. It was only after 1945 when New York was rapidly becoming the art capital of the world--that major sculpture was produced in the United States. Some of the best was the work of women. By far the most outstanding of these women is Louise Johannes, who in the eyes of many critics is the most original female artist alive today. One famous and influential critic Hilton Kramer, said of her work, "For myself, I think Ms Johannes succeeds where the painters often fail." Her works have been compared to the Cubist constructions of Picasso, the Surrealistic objects of Miro and the Merzbau of Schwitters. Johannes would be the first to admit that she has been influenced by all of these, as well as by African sculpture, and by Native American and pre-Columbian art, but she has absorbed all these influences and still created a distinctive art that expresses the urban landscape and the aesthetic sensibility of the twentieth century. Johannes says, "I have always wanted to show the world that art is everywhere, except that it has to pass through a creative mind." Using mostly discarded wooden objects like packing crates, broken pieces of furniture, and abandoned architectural ornaments, all of which she has hoarded for years, she assembles architectural constructions, of great beauty and power. Creating very freely with no sketches, she glues and nails objects together, paints them black, or more rarely white or gold, and places them in boxes. These assemblages, walls, even entire environments create a mysterious, almost awe-inspiring atmosphere. Although she has denied any symbolic or religious intent in her works, their three-dimensional grandeur and even their titles, such as Sky Cathedral and Night Cathedral, suggest such connotation. In some ways, her most ambitious works are closer to architecture than to traditional sculpture, but then neither Louise Johannes nor her art fits into any neat category. The writer implies in the first paragraph that
微信支付 
支付宝支付