题目内容
Tomorrow the weather will be changing for the better in ______.
查看答案
搜索结果不匹配？点我反馈
更多问题
GENETICALLY MODIFIED FOODS
Are genetically modified crops an environmental dream come-true or a disaster in the making？ Scientists are looking for answers.
The world seems increasingly divided into those who favor genetically modified(GM) foods and those who fear them Advocates assert that growing genetically altered crops can be kinder to the environment and that eating foods from those plants is perfectly safe. And, they say genetic engineering which can induce plants to grow in poor soils or to produce more nutritious foods will soon become an essential tool for helping to feed the world's burgeoning population. Skeptics contend that GM crops could pose unique risks to the environment and to health risks too troubling to accept placidly, Taking that view, many European countries are restricting the planting and importation of GM agricultural products. Much of the debate hinges on perceptions of safety. But what exactly does recent scientific research say about the hazards？ The answers, too often lost in reports on the controversy, are served up in the pages that follow.
Two years ago in Edinburgh, Scotland, eco-vandals stormed a field, crushing canola plants. Last year in Maine, midnight raiders hacked down more than 3000 experimental poplar trees. And in Sun Diego, protesters smashed sorghum and sprayed paint over greenhouse walls.
This far-flung outrage took aim at genetically modified crops. But the protests backfired: all the destroyed plants were conventionally bred. In each case, activists mistook ordinary plants for GM varieties.
It's easy to understand why. In a way, GM crops—now on some 109 million acres of farmland worldwide—are invisible. You can't see, taste or touch a gene inserted into a plant or sense its effects on the environment. You can't tell, just by looking, whether pollen containing a foreign gene can poison butterflies or fertilize plants miles away. That invisibility is precisely what worries people. How, exactly, will GM crops affect the environment—and when will we notice？
Advocates of GM, or transgenic, crops say the plants will benefit the environment by requiting fewer toxic pesticides than conventional crops. But critics fear the potential risks and wonder how big the benefits really are. "We have so many questions about these plants," remarks Guenther Stotzky, a soil microbiologist at New York University. "There's a lot we don't know and need to find out."
As GM crops multiply in the landscape, unprecedented numbers of researchers have started fanning into the fields to get the missing information. Some of their recent findings are reassuring; others suggest a need for vigilance.
Fewer Poisons in the Soil？
Every year U.S. growers shower crops with an estimated 971 million pounds of pesticides, mostly to kill insects, weeds and fungi. 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 began advertising GM seeds that promised to reduce a farmer's use of toxic pesticides. Today most GM crops-mainly soybean, com, cotton and canola-contain genes enabling them to either resist insect pests or tolerate weed-killing herbicides. The insect-resistant varieties make their own insecticide, a property meant to reduce the need for chemical sprays. The herbicidetolerant types survive when exposed to broad-spectrum weed killers, potentially allowing farmers to forgo more poisonous chemicals that target specific weed species. Farmers 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.
&
A．4,000 5,100.B．4,000 1,500.C．14,000 1,500.D．4,000 2,500.
Bringing up children is a hard work, and you are often to blame for any bad behavior. of your children, If so, Judith Rich Harris has good news for you. Parents, she argues, have no important long-term effects on the development of the personality of their children. Far more important are their playground friends and neighborhood. Ms. Harris takes to hitting the assumption, which has dominated developmental psychology for almost half a century.
Ms. Harris's attack on the developmentalists' "nature" argument looks likely to reinforce doubts that the profession was already having. If parents matter, why is it that two adopted children, reared in the same home, are no more similar in personality than two adopted children reared in separate homes？ Or that a pair of identical twins, reared in the same home, are no more alike than a pair of identical twine reared in different homes？
Difficult as it is to track the precise effects of parental upbringing, it may be harder to measure the exact influence of the peer(同龄人) group in childhood and adolescence. Ms. Harris points to how children from immigrant homes soon learn not to speak at school in the way their parents speak. But acquiring a language is surely a skill, rather than a characteristic of the sort developmental psychologists hunt for. Certainly it is different from growing up tensely or relaxed, or from learning to be honest or hard-working or generous. Easy though it may be to prove that parents have little impact on those qualities, it will be hard to prove that peers have vastly more.
Moreover, mum and dad surely cannot be ditched completely. Young adults may, as Ms. Harris argues, be keen to appear like their peers. But even in those early years, parents have the power to open doors: they may initially choose the peers with whom their young associate, and pick that influential neighborhood. Moreover, most people suspect that they come to resemble their parents more in middle age, and that people's child bearing habits may be formed partly by what their parents did. So the balance of influences is probably complicated, as most parents already suspected without being able to demonstrate it scientifically. Even if it turns out that the genes they pass on and the friends their children play with matter as much as affection, discipline and good example, parents are not completely off the hook.
According to Ms. Harris, ______.
【B10】
微信支付 
支付宝支付