Part IV Reading Comprehension (Reading in Depth) (25 minutes)

　　Section A

　　Directions: In this section, there is a short passage with 5 questions or incomplete statements. Read the passage carefully. Then answer the questions or complete the statements in the fewest possible words on Answer Sheet 2.

　　Questions 47 to 51 are based on the following passage.

　　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 Bj?rn 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 Fouchier, 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 H5N1 strain of bird flu?"

　　In poultry avian viruses can mutate(变异)into more virulent influenza strains, including H5N1. 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.

　　47. According to the author, what may be the possible carriers of bird flu?

　　48. The main sources of influenza viruses in lake water are ________, which may stay infectious for up to 30 days.

　　49. By saying "bird flu viruses appear to exist in ducks in a low-pathogenic form" (Para. 6), the author suggests that infection ________.

　　50. On what condition can the birds spread the influenza through migration?

　　51. According to the study team, ________ is a practice that can encourage transmission of the bird flu.

　　Section B

　　Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked [A], [B], [C] and [D]. You should decide on the best choice and mark the corresponding letter on Answer Sheet 2 with a single line through the center.

　　Passage One

　　Questions 52 to 56 are based on the following passage.

　　For about three centuries we have been doing science, trying science out, using science for the construction of what we call modern civilization. Every dispensable item of contemporary technology, from canal locks to dial telephones to penicillin, was pieced together from the analysis of data provided by one or another series of scientific experiments. Three hundred years seems a long time for testing a new approach to human inter-living, long enough to set back for critical appraisal of the scientific method, maybe even long enough to vote on whether to go on with it or not. There is an argument.

　　Voices have been raised in protest since the beginning, rising in pitch and violence in the nineteenth century during the early stages of the industrial revolution, summoning urgent crowds into the streets on the issue of nuclear energy. "Give it back," say some of the voices, "It doesn't really work, we've tried it and it doesn't work. Go back three hundred years and start again on something else less chancy for the race of man."

　　The principle discoveries in this century, taking all in all, are the glimpses of the depth of our ignorance of nature. Things that used to seem clear and rational, and matters of absolute certainty-Newtonian mechanics, for example-have slipped through our fingers; and we are left with a new set of gigantic puzzles, cosmic uncertainties, and ambiguities. Some of the laws of physics are amended every few years; some are canceled outright; some undergo revised versions of legislative intent as if they were acts of Congress.

　　Just thirty years ago we call it a biological revolution when the fantastic geometry of the DNA molecule was exposed to public view and the linear language of genetics was decoded. For a while, things seemed simple and clear: the cell was a neat little machine, a mechanical device ready for taking to pieces and reassembling, like a tiny watch. But just in the last few years it has become almost unbelievably complex, filled with strange parts whose functions are beyond today's imagining.

　　It is not just that there is more to do, there is everything to do. What lies ahead, or what can lie ahead if the efforts in basic research are continued, is much more than the conquest of human disease or the improvement of agricultural technology or the cultivation of nutrients in the sea. As we learn more about fundamental processes of living things in general we will learn more about ourselves.

　　52. What CANNOT be inferred from the first paragraph?

　　[A] Scientific experiments in the past three hundred years have produced many valuable items.

　　[B] For three hundred years there have been people holding a hostile attitude toward science.

　　[C] Modern civilization depends on science so man supports scientific progress unanimously.

　　[D] Some people think three hundred years is not long enough to set back for critical appraisal of scientific method.

　　53. The principle discovery in this century shows ________.

　　[A] man has overthrown Newton's laws of physics

　　[B] man has solved a new set of gigantic puzzles

　　[C] man has lost many scientific discoveries

　　[D] man has given up some of the once accepted theories

　　54. Now scientists have found in the past few years ________.

　　[A] the exposure of DNA to the public is unnecessary

　　[B] the tiny cell in DNA is a neat little machine

　　[C] man knows nothing about DNA

　　[D] man has much to learn about DNA

　　55. The writer's main purpose in writing the passage is to say that ________.

　　[A] science is just at its beginning

　　[B] science has greatly improved man's life

　　[C] science has made profound progress

　　[D] science has done too little to human beings

　　56. The writer's attitude towards science is ________.

　　[A] critical [B] approving [C] neutral [D] regretful

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