星火：2008年12月英语四级模拟试卷样题及解析

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　　Part Ⅰ Writing (30 minutes)

　　Directions: For this part, you are allowed 30 minutes to write a short essay entitled The Decrease of Public Transportation Ticket Fare. You should write at least 120 words following the outline given below:

　　1. 近来一些城市政府实施多项举措降低公共交通票价，大力发展公共交通;

　　2. 此措施带来的好处;

　　3. 作为市民应如何响应政府的号召。

　　The Decrease of Public Transportation Ticket Fare

　　Part Ⅱ Reading Comprehension (Skimming and Scanning)(15 minutes)

　　Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1.

　　For questions 1-7,choose the best answer from the four choices marked A), B), C) and D).

　　For questions 8-10,complete the sentences with the information given in the passage.

　　The Debate Over Genetically Modified Foods

　　For thousands of years farmers have used a process of selection and cross breeding to continually improve the quality of crops. Traditional breeding methods are slow, requiring intensive labor: while trying to get a desirable trait in a bred species, undesirable traits will appear and farmers must continue the process over and over again until all the undesirables are bred out. In contrast, organisms acquire one specific gene or a few genes together through genetic modification, without other traits included and within a single generation. However, this technology too is inherently unpredictable and some scientists believe it can produce potentially dangerous results unless better testing methods are developed. Traditional breeding is based on sexual reproduction between like organisms. The transferred genes are similar to genes in the cell they join. They are conveyed in complete groups and in a fixed sequence that harmonizes with the sequence of genes in the partner cell. In contrast, bioengineers isolate a gene from one type of organism and collect it randomly into the DNA of a dissimilar species, disrupting its natural sequence. One of the main differences between conventional and genetically modified crops is that the former involves crosses either within species or between very closely related species. However, GM crops can have genes from closely related species or even from bacteria and viruses. Benefits: one side of the debate Economical? GM supporters tell farmers that they stand to reap enormous profits from growing GM crops. It takes a shorter time to produce the desired product. It is precise and there are no unwanted genes. To produce the GM crops, modern biotechnology is used which requires highly skilled people and sophisticated and expensive equipment. Large companies need considerable investments in laboratories, equipment and human resources, hence the reason why GM crops are more expensive for farmers than traditional crops. Herbicide-resistant crops So what other advantages do GM crops hold for farmers? GM crops can be produced to be herbicide (除草剂) resistant. This means that farmers could spray these crops with herbicide and kill the weeds, without affecting the crop. In effect, the amount of herbicide used in one season would be reduced, with a subsequent reduction in costs for farmers and consumers. Biotechnology companies are even experimenting with crops that can be genetically modified to be drought and salt-tolerant, or less reliant on fertilizer, opening up new areas to be farmed and leading to increased productivity. However, the claims of less herbicide usage with GM crops have till now not been independently supported by facts. Better quality foods Even animals can be genetically modified to be leaner, grow faster, and need less food. They could be modified to have special characteristics, such as greater milk production in cows. These modifications again lead to improved productivity for farmers and finally lower costs for the consumers. Modified crops could perhaps prevent outbreaks such as foot and mouth disease, which has badly influenced many farmers and local economies. No such products have been released to date; however, some are under consideration for release. For example, GM salmon, capable of growing almost 30 times faster than natural salmon, may soon be approved by the FDA (Food and Drug Administration) in the U.S. for release into open waters without a single study on the impact on human health or the environment. Risks: the other side of the debate Environmental damage The problem with GM crops is that there is little known about what effect they will have in, say, 20 years time. The genetic structure of any living organism is complex and GM crop tests focus on short-term effects. Not all the effects of introducing a foreign gene into the complex genetic structure of an organism are tested. Will the pests that a crop was created to resist eventually become resistant to this crop? Then there is always the possibility that we may not be able to destroy GM crops once they spread into the environment. Risk to food web. A further complication is that the pesticide produced in the crop may unintentionally harm creatures. GM crops may also pose a health risk to native animals that eat them. The animals may be poisoned by the built-in pesticides. Tests in the U.S. showed that 44% of caterpillars (毛虫) of the monarch butterfly died when fed large amounts of pollen(花粉)from GM corn. Disease. Another concern is disease. Since some crops are modified using the DNA from viruses and bacteria, will we see new diseases emerge? What about the GM crops that have antibiotic-resistant marker genes? Marker genes are used by scientists to determine whether their genetic modification of a plant was successful. Will these antibiotic-resistant genes be transferred to microorganisms that cause disease? We already have a problem with ineffective antibiotics. How can we develop new drugs to fight these new bugs? Until further studies can show that GM foods and crops do not pose serious threats to human health or the world's ecosystems, the debate over their release will continue. Living organisms are complex and tampering with their genes may have unintended effects. It is in our common interest to support concerned scientists and organizations, such as Friends of the Earth who demand required labeling of these food products and independent testing for safety and environmental impacts.

　　1. What is the main difference between conventional breeding and genetic breeding?

　　A) The former is based on sexual reproduction between like organisms while the latter can have genes even from bacteria and viruses.

　　B) The former is unpredictable while the latter is predictable.

　　C) The former is applied by farmers while the latter by scientists.

　　D) The former has a long history while the latter a short one.