四六级考试

【单选题】TheDebate over Genetically Modified Foods--Rice with built-in Vitamin
A、that can help prevent blindness in 100 million children suffering from Vitamin
A、deficiency--
A、tomato (hat softens more slowly, allowing it to develop longer on the vine and keep longer on the shelf--Potatoes that absorb less fat when fried, changing the ever-popular French fries from junk food into a more nutritional food--Strawberry crops that can survive frostThese are some of the benefits promised by biotechnology. The debate over its benefits and safety, however, continues.Do we really need to fear mutant (突变体) weeds, killer tomatoes, and giant corn and will the benefits be delivered ConventionalBreeding Versus Genetically Modified (GM)CropsFor thousands of years farmers have used a process of selection and cross breeding to continually improve the quality of crops.Even in nature, plants and animals selectively breed, thus ensuring the optimum gene pool for future generations. Traditional breeding methods are slow, requiring intensive labor: While trying to get a desirable trait in a bred species, undesirable traits will appear and breeders 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 splice (接合) it haphazardly into theDN
A、of a dissimilar species, disrupting its natural sequence. Further, because the transplanted gene is foreign to its new surroundings, it cannot adequately function without a big artificial boost.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. GM crops can have genes either from closely related species or from distant species, even bacteria and viruses. Benefits: One Side of theDebate--Economical benefitsGM supporters tell farmers that they stand to reap enormous profits from growing GM crops. Initially, the cost is expensive but money is saved on pesticides. 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. GM crops, farmers are told, are a far better option. It takes a shorter time to produce the desired product. It is precise and there are no unwanted genes.--Herbicide-ResistantCropsSo what other advantages do GM crops hold for farmers GM crops can be produced to be herbicide-resistant. This means that farmers could spray these crops with herbicide and kill the weeds, without affecting the crops. In effect, the amount of herbicide used in one season would be reduced, with a subsequent reduction in costs for farmers and consumers. For Ingard cotton, pest-resistance was built into the cotton, hence reducing and even removing the use of pesticides, which are not only expensive but, more importantly, harmful to the environment. 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. How
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主旨题 根据关键词this article tells us可知此题考查的是文章的主旨。查读小标题Conclusion下面最后一段…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． document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>