题目内容
The Debate 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 that 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 frost
These 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 com and will the benefits be delivered？
Conventional Breeding Versus Genetically Modified (GM) Crops
For 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 the DNA 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 the Debate
？Economical benefits
GM 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-Resistant Crops
So 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 c
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As a result of the recent energy crisis, new concepts for creating HDR recovery systems— which involve drilling holes and connecting them to artificial reservoirs placed deep within the crust—are being developed. In all attempts to retrieve energy from HDR's artificial stimulation will be required to create either sufficient permeability or bounded flow paths to facilitate the removal of heat by circulation of a fluid over the surface of the rock.
The HDR resource base is generally defined to include crustal rock that is hotter than 150℃, is at depths less than ten kilometers, and can be drilled with presently available equipment. Although wells deeper than ten kilometers are technically feasible, prevailing economic factors will obviously determine the commercial feasibility of wells at such depths. Rock temperatures as low as 100℃ may be useful for space heating; however, for producing electricity, temperatures greater than 200℃ are desirable. The geothermal gradient, which specifically determines the depth of drilling required to reach a desired temperature, is a major factor in the recoverability of geothermal resources. Temperature gradient maps generated from oil and gas well temperature-depth records kept by the American Association of Petroleum Geologists suggest that tappable high-temperature gradients are distributed all across the United States. (There are many areas, however, for which no temperature gradient records exist. )
Indications are that the IIDR resource base is very large. If an average geothermal temperature gradient of 22℃ per kilometer of depth is used, a staggering 13,000,000 quadrillion B. T. U's of total energy are calculated to be contained in crustal rock to a ten kilometer depth in the United States. If we conservatively estimate that only about O. 2 percent is recoverable, we find a total that is comparable to the estimated resource base of all the coal remaining in the United States. The remaining problem is to balance the economics of deeper, hotter, more costly wells and shallower, cooler, less expensive wells against the value of the final product, electricity and/or heat.
The primary purpose of the passage is to______.
In a perfectly free and open market economy, the type of employer—government or private-should have little or no impact on the earnings differentials between women and men. However, if there is discrimination against one sex it is unlikely that the degree of discrimination by government and private employers will be the same. Differences in the degree of discrimination would result in earnings differentials associated with the type of employer. Given the nature of government and private employers, it seems most likely that discrimination by private employers would be greater. Thus, one would expect that, if women are being discriminated against, government employment would have a positive effect on women's earnings as compared with their earnings from private employment. The results of a study by Fuchs support this assumption. Fuchs's results suggest that the earnings of women in an industry composed entirely of government employees would by 14. 6 percent greater than the earnings of women in industry composed exclusively of private employees, other things being equal.
In addition, both Fuchs and Sanborn have suggested that the effect of discrimination by consumers on the earnings of self-employed women may be greater than the effect of either government or private employer discrimination on the earnings of women employees. To test this hypothesis, Brown selected a large sample of white male and female workers from the 1970 Census and divided them into three categories: private employees, government employees, and self-employed. (Black workers were excluded from the sample to avoid picking up earnings differentials that were the result of racial disparities. ) Brown's research design controlled for education, labor-force participation, mobility, motivation, and age in order to eliminate these factors as explanations of the study's results. Brown's results suggest that men and women are not treated the same by employers and consumers. For men, self-employment is highest earnings category, with private employment next, and government lowest. For women, this order is reversed.
One can infer from Brown's results that consumers discriminate against self-employed women. In addition, self-employed women may have more difficulty than men in getting good employees and may encounter discrimination from suppliers and from financial institutions.
Brown's results are clearly consistent with Fuchs's argument that discrimination by consumers has a greater impact on the earnings of women than does discrimination by either government or private employers. Also, the fact that women do better working for government than for private employers implies that private employers are discriminating against women. The results do not prove that the government does not discriminate against women. They do, however, demonstrate that if government is discriminating against women, its discrimination is not having as much effect of women's earnings as is discrimination in the private sector.
The passage mentions all of the following as difficulties that self-employed women may encounter EXCEPT______.
听力原文：W. I'd like to make an appointment with Prof. Winston tomorrow.
M: I'm sorry. Prof. Winston went on a one-week vacation in Hong Kong. He'll probably be back next weekend.
(16)
This article tells us that further studies are needed to assess the potential risks of GM
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