2. 职称英语
  3. Every year U. S. growers shower crops with an estimated 971 million pounds o

Every year U. S. growers shower crops with an estimated 971 million pounds o

游客2023-08-29  53
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? [br] What is the advantage of GM seeds according to the passage?
选项 A、They can be sowed more easily and quickly.
B、They don’t need to be sprayed with pesticides.
C、They make the pesticide applications simpler than before.
D、Less seeds are required for the land of a certain size.
答案 C
解析 事实细节题。第二段提到了基改种子的很多优点，其中包括：降低有毒农药的用量；可以摒弃针对特定杂草且毒性更强的化学药剂；简化了劳作手续：使产量增加。[C]项为优点之一，故为答案。[A]、[D]没有提及；[B]和原文不符。
转载请注明原文地址:http://tihaiku.com/zcyy/2967002.html
相关试题推荐
随机试题
最新回复(0)