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  3. Every year U. S. growers shower crops with an estimated 971 million pounds of pesticides, mostly to kill insects and weeds. But

Every year U. S. growers shower crops with an estimated 971 million pounds of pesticides, mostly to kill insects and weeds. But

admin2013-07-02  15
问题     Every year U. S. growers shower crops with an estimated 971 million pounds of pesticides, mostly to kill insects and weeds. But pesticide residues linger on crops and the surrounding soil, leaching into groundwater, running into streams and getting gobbled up by wildlife. The constant chemical trickle is an old worry for environmentalists.

    In the mid-1990s agribusinesses(农业综合企业)began advertising GM seeds that promised to reduce a farmer’s use of toxic pesticides. Today most GM crops — mainly soybean, corn and cotton — contain genes enabling them to either resist insect pests or tolerate weed-killing herbicides(除草剂). The insect-resistant varieties make their own insecticide, a property meant to reduce the need for chemical sprays. The herbicidetoler-ant types survive when exposed to broad-spectrum weed killers, potentially allowing farmers to forgo more poisonous chemicals that target specific weed species. Farmers like to limit the use of more hazardous pesticides when they can, but GM crops also hold appeal because they simplify operations(reducing the frequency and complexity of pesticide applications)and, in some cases, increase yields.
    But confirming environmental benefit is tricky. Virtually no peer-reviewed papers have addressed such advantages, which would be expected to vary from plant to plant and place to place. Some information is available, however. According to the U. S. Department of Agriculture, farmers who plant herbicidetolerant crops do not necessarily use fewer sprays, but they do apply a more benign mix of chemicals.
    Insect-resistant crops also bring mixed benefits. To date, insect resistance has been provided by a gene from the soil bacterium Bacillus thuringiensis(Bt). This gene directs cells to manufacture a crystalline protein that is toxic to certain insects but does not harm other organisms. The toxin gene in different strains of Bt can affect different mixes of insects, so seed makers can select the version that seems best suited to a particular crop.
    Defining the environmental risks of GM crops seems even harder than calculating their benefits. At the moment, public attention is most trained on Bt crops, thanks to several negative studies. Regulators, too, are surveying the risks intensely. This spring or summer the EPA is expected to issue major new guidelines for Bt crops, ordering seed producers to show more thoroughly that the crops can be planted safely and monitored in farm fields.
    In the face of mounting consumer concern, scientists are stepping up research into the consequences of Bt and other GM crops. Among their questions: How do Bt crops affect "nontarget" organisms — the innocent bugs, birds, worms and other creatures that happen to pass by the modified plants? Will GM crops pollinate nearby plants, casting their genes into the wild to create superweeds that grow unchecked? What are the odds that the genetically engineered traits will lose their ability to protect against insects and invasive weeds, leaving GM plants suddenly vulnerable?
What can we know about Bt?
选项 A、Bt has escaped the public’s attention and criticism.
B、Bt has been questioned or even criticized by the public.
C、There was no official regulation on Bt in the past.
D、Bt is a powerful chemical pesticide to weeds or pests.
答案B
解析 推理判断题。有关Bt的信息出现在文章的第四、五段。由于出现了几份负面报告，大众开始关注Bt，政府也开始评估基改作物的风险，由此推断，这些负面报告是和Bt有关的，选项[B]正确。[A]显然和事实相反；[C]文章说发布新规定，则以前还是存在一些规定的，显然错误；[D]原文是说Bt会产生对某些昆虫有害的毒性，但这与chemical pesticide是有区别的，而且不针对weeds，故错误。
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