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Countless people are born with(生来就具有某种特点)the susceptibility to inherit a genetic disease. But scientific progress, especially the art of interfering with(干涉,阻碍) the genetic makeup of the human body, has helped doctors prevent more and more inherited disorders in the last decade.Dr. Thomas Caskey of the Baylor University College of medicine in Houston, Texas, is a pioneer in molecular biology(分子生物学). Through the techniques of genetic engineering(基因工程), he transfers genes from one organism to another. Caskey uses a certain type of virus, called a retrovirus(逆转录病毒), as the vehicle for the gene transfer. He first cripples the virus by removing the portion it needs to reproduce itself. The crippled virus becomes harmless while still being able to deliver a cargo to its destination.The cargo in Caskey’s experiment is the human A-D-A gene, taken from bone marrow. A-D-A stands for(代表) adenosine deaminase(腺苷脱氨酶), an important component of the human immune system. A defect in the A-D-A gene leads to immune deficiency, rendering(致使) the body defenseless against infections. Caskey’s purpose was to see if the human A-D-A gene could repair the defective immune system of a mouse.In the experiment the mouse was given a dose of radiation heavy enough to destroy its immune system. The animal next was injected with the crippled virus carrying the human A-D-A gene. According to Caskey, "the mouse will die within 10 to 14 days unless a successful transfer of bone marrow cells takes place. So we lethally irradiate and subsequently rescue the mouse by bone marrow transplantation(骨髓移植)with the cells that have been infected with the virus." The mouse now carries the human gene that salvaged its immune system.Bone marrow transplantation has an established place in contemporary medical practice. Employed to restore the immune system of certain cancer patients and of people who have been exposed to radiation, bone marrow transplantation works only if there is a good match between donor and recipient.The procedure would be much easier if bone marrow were like blood. People with type O blood are universal donors(万能供体). Their blood may be transfused to those who have different blood types. Unfortunately, there is no such thing as a universal bone-marrow type. Researchers may have found a way, however, to overcome this problem. The solution, if it works, would be to implant the patient with his own, perfectly matching(型配), bone marrow.The idea, as Caskey explains it, is to "correct the patient’s disease with his own ceils, but those cells have added to them a normally functioning gene. "In other words, surgeons would take defective bone-marrow cells from the patient and put them into a laboratory dish where the cells would be exposed to a crippled virus carrying a healthy AD-A gene from a donor. The A-D-A gene would repair the defective cells and then the cells would be reinjected into the patient. Thus, in Caskey words, "the patient would be transplanted by his own ceils containing the added normal gene."The technique sounds deceptively(靠不住地) simple. In reality, though(可是,不过, 然而), it is complex. A number of laboratories have tested various intermediate steps of the process, but, according to Caskey, "no single laboratory has put together the entire technology successfully, and highly reproducibly, to proceed with a gene transfer at-tempt in man."For some time now, the U.S. National Institute of Health has been taking a close look at(仔细,研究) the effectiveness and safety of the procedure, as well as the ethical questions it raises. There doesn’t seem to be much concern about the ethics of gene transfer into a human being to correct a genetic defect.Dr. W. French Anderson of N. I. H. wrote recently that "claims that new organs, designed personalities, master races, or Frankenstein(佛兰肯思泰因，一个创造怪物而自己被它毁灭的医学研究者，英国女作家Mary W.Shelly同名小说中的主角) monsters will be created can be given no credence in the light of(根据,从……来看) what is presently known. "And he added that a well-informed public is the best assurance against any future misuses of genetic engineering. Where is the A-D-A gene taken from in Caskey’s experiment（）
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William, who conquered England some 930 years ago, had wealth, power and a ruthless army. Yet although William was stupefyingly rich by the standard of his time, he had nothing remotely resembling a flush toilet. No paper towels, no riding lawn mower. How did he get byHistory books are filled with wealthy people who were practically destitute compared to me, I have tripe-tracked storm window; Croesus did not. Entire nations trembled before Alexander the Great, but he couldn’t buy cat food in bulk. Czar Nicholas Ⅱ lacked a compound-miter saw.Given how much better off I am than so many famous dead people, you’d think I’d be content. The trouble is that, like most people, I compare my prosperity with that of living persons: neighbors, high-school classmates, TV personalities. The covetousness I feel toward my friend Howard’s kitchen is not mitigated by the fact that no French monarch ever had a refrigerator with glass doors.There is really no rising or falling standard of living. Over the centuries people simply find different stuff to feel grumpy about. You’d think that merely not having bubonic plague(腺鼠疫) would put us in a good mood. But no, we want a hot tub too.Of course, one way to achieve happiness would be to realize that even by contemporary standards the things I own are pretty nice. My house is smaller than the houses of many investment bankers’, but even so it has a lot more rooms than my wife’s and I can keep clean. Besides, to people looking back at our era from a century or two in the future, those bankers’ fancy counter tops and my own worn Formica(福米加塑料桌面)will seem equally shabby. I can’t keep up with my neighbor right now. but just wait. The underlined word "destitute" (Para.2)means（）
Between now(June) and Labor Day, millions of American will offer up their bodies to the sun’s rays. A tan indicates health and beauty, and most sun worshippers will sacrifice a lot to achieve it—including themselves. With each hour, the sun’s ultraviolet radiation produces irreversible damage, hastening the development of unsightly wrinkles. And with each year on the beach or rooftop, the sunbather increases his risk of getting skin cancer.Skin cancer is by far the most common form of cancer. An estimated 400000 new cases will be detected this year in the United States, and almost all of them can be blamed on overexposure to the sun. Fortunately, most of these cancers are highly curable. But they can be disfiguring and take time to treat. For that reason, sun worshippers should treat deity with a good deal of awe.Sunburn, of course, is the initial hazard posed by UV radiation. Prolonged exposure to UV, however, interferes with the production of collagen fibers in the dermis, causing the skin to lose elasticity and creating premature wrinkles. Further deterioration of the dermis deprives the epidermis of nutrition and causes it to become thin and dry.Cancer is UV’s final insult. Short-wave radiant energy, especially from the UV-B band, breaks the strands of DNA. Enzymes work constantly to rearrange the DNA into proper sequence, but with repeated UV exposure, the repair process may eventually break down. Then the mutant DNA may produce a colony of cancer cells.But skin cancer may be avoided with a good dose of common sense. People with fair skin and blue eyes who burn easily stand the highest risk. Special danger spots are the parts of the body most constantly exposed to the sun, such as the cheeks, nose, lower lip and the ears. People who have already developed precancerous lesions or had one skin cancer growth stand a greatly increased chance of developing others. Dermatologists recommend avoiding the sun when it is most intense—between 11 a.m. and 3 p.m. Anyone who insists on sunbathing should use a good sun screen. These lotions and salves contain chemicals, such as paraaminobenzoic acid, that block out the burning UV-B radiation while permitting the tanning rays to reach the skin. According to the passage, overexposure to the sun may result in（）
People around the globe hit the height of their misery and depression in (51) age, a new international study suggests.The finding by British and American researchers was based on an analysis of well-being among approximately 2 million people in 80 nations. With few exceptions, the observation appears to apply across the board, regardless (52) gender, culture, geography, wealth, job history, education, and marriage or parental status."The scientific fact seems to be that happiness and positive mental health follow a giant ’U’ (53) through life, " said study author Andrew J. Oswald, a professor of economics at Warwick University in Warwickshire, England. "For the average person, it’s high when you’re 20, and then it slowly falls and bottoms out (54) your 40s. But the good news is that your (55) health picks up again, and eventually gets back to the high levels of our youth. "The finding was (56) on the pooling of several different sources of happiness data, including: two multi-decade happiness/satisfaction surveys (first launched in the 1970s), involving about 500,000 American and Western European men and women; four rounds of the 80-nation "World Values Survey" (57) between 1981 and 2004 in North America, Eastern and Western Europe, Asia, Africa, Australia, and Central and South America; and a 2004—2007 survey (58) nearly 1 million Britons.The bottom-line: For most people throughout the world, the highest probability for depression striking is around 44 years of (59) .In the United States, however, some as-yet unexplained (60) differences were observed, with happiness among men dipping the most in their early 50s, whereas women hit their Nadir around the age of 40.The researchers cautioned that cheerful people tend to live longer than unhappy (61) —a fact that might have skewed the overall finding. But they also suggested that evidence of a happiness (62) might simply reflect a midlife choice to give up long-held but no longer tenable aspirations, followed by a senior’s sense of gratitude for having successfully endured (63) others did not."That said, some might find it helpful simply to understand the general (64) of mental health as they go through their own life," said Oswald. "It might be useful for people to realize that if they are (65) in their 40s, this is normal, it is not exceptional. And just knowing this might help. " 55.（）
被疟原虫寄生的红血球在人体内的存在时间不会超过120天。因为疟原虫不可能从一个它所寄生的衰亡的红血球进入一个新生的红血球。因此，如果一个疟疾患者在进入了一个绝对不会再被疟蚊叮咬的地方120天后仍然周期性高烧不退，那么，这种高烧不会是由疟原虫引起的。 以下哪项，如果为真，最能削弱上述结论
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