首页
登录
职称英语
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
9
管理
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] From the passage, we can learn that plants which can tolerate herbicide______.
选项
A、need no chemical pesticides in the whole process of maturing
B、need less chemical pesticides as they were advertised before
C、can turn out some certain chemical pesticides by themselves
D、require gentle chemicals and simple planting as well
答案
D
解析
事实细节题。第三段指出基改植物“对环境有好处”却不易证实。但还是有资料表明:耐除草剂的作物不见得会降低农药的喷洒量,不过农民确实在使。用比较温和的混合药剂,第二段提到基改种子简化了劳作程序,使种植简单了。所以选项[D]正确。其他选项都与文章所提的事实不符。
转载请注明原文地址:https://tihaiku.com/zcyy/2967003.html
相关试题推荐
[originaltext]W:Today,millionsofusarenowaddictedtochatrooms,e-maila
Amillionmotoristsleavetheircarsfilledupwithpetrolandwiththekeys
Amillionmotoristsleavetheircarsfilledupwithpetrolandwiththekeys
Amillionmotoristsleavetheircarsfilledupwithpetrolandwiththekeys
Amillionmotoristsleavetheircarsfilledupwithpetrolandwiththekeys
Amillionmotoristsleavetheircarsfilledupwithpetrolandwiththekeys
EverySundaymorningmillionsofIndianssettledownwithacupofteaandth
EverySundaymorningmillionsofIndianssettledownwithacupofteaandth
EverySundaymorningmillionsofIndianssettledownwithacupofteaandth
EverySundaymorningmillionsofIndianssettledownwithacupofteaandth
随机试题
(1)Inadecadeworkingasananny,AndreiaSoaresfinallyclamberedupthel
[originaltext]W:Youaregoingtogiveashortspeechofthanksforthespeaker
Cubesaren’tusuallythego-toshapewhencreatinganobjectthat’smeantto
ItIsn’tEasyBeingGreenGreenstoriesofhotelsA
对
活动义齿修复模型设计固位体时所依据的是A.横曲线 B.纵曲线 C.外形高点线
患儿,2岁,因咳嗽2d,喘憋半天入院,体检:T38.4℃,脉率96次/min,呼
(2016年)下列各项中,属于国家审计机关权限的有:A.检查被审计单位财务收支电
体内维生素E主要贮存在( )。A.肝脏 B.肾脏 C.骨骼 D.肌肉
关于患者享有平等医疗权利的表述中,错误的是A.公民享有生命健康权 B.对所有患
最新回复
(
0
)