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听力原文：M: You call Mary a dreamer, but I think she has many good ideas.
W: Good ideas are only useful if you can make something out of them.
Q: Why does the woman think Mary is a dreamer？
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Even genes from animals can be used to engineer crops.
The common cold is the world's most widespread illness, which is probably why there are more myths about it than any of the other plagues that flesh is heir to.
The most widespread fallacy of all is that colds are caused by cold. They are not. They are caused by viruses passed on from person to person. You catch a cold by coming into contact, directly or indirectly, with someone who already has one. If cold causes colds, it would be reasonable to expect the Eskimos to suffer from them permanently. But they do not. And in isolated arctic regions explorers have reported being free from colds until coming into contact again with infected people from the outside world by way of packages and mail dropped from airplanes.
During the First World War, soldiers who spent long periods in the trenches, cold and wet, showed no increased tendency to catch colds.
In the Second World War, prisoners at the notorious Auschwitz concentration camp, naked and starving, were astonished to find that they seldom had colds.
At the Common Cold Research Unit in England, volunteers took part in experiments in which they submitted to the discomforts of being cold and wet for long stretches of time. After taking hot baths, they put on bathing suits, allowed themselves to be doused with cold water, and then stood about dripping wet in drafty rooms. Some wore wet socks all day while others exercised in the rain until close to exhaustion. Not one of the volunteers came down with a cold unless a cold virus was actually dropped in his nose.
If, then, cold and wet have nothing to do with catching colds, why are they more prevalent in the winter？ Despite the most painstaking research, no one has yet found the answer. One explanation offered by scientists is that people tend to stay together indoors more in cold weather than at other times, and this makes it easier for cold viruses to be passed on.
No one has yet found a cure for colds. There are drugs and pain suppressors such as aspirin, but all they do is to relieve the symptoms.
According to the passage, there are more myths about the common cold than any other human disease because ______.
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
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______.
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