It is no secret among athletes that in order to improve performa    For years, doctors advised their patients that the only thing taking multivitamins does is give them extensive urine (尿). After all, true vitamin deficiencies are practically unheard of in industrialized countries. Now it seems those doctors may have been wrong. The results of a growing number of studies suggest that even a modest vitamin shortfall can be harmful to your health. Although proof of the benefits of multivitamins is still far from certain, the few dollars you spend on them is probably a good investment.
　　Or at least that's the argument put forward in the New England Journal of Medicine. Ideally, say Dr. Walter Willett and Dr. Meir Stampfer of Harvard, all vitamin supplements would be evaluated in scientifically rigorous clinical trials.
　　But those studies can take a long time and often raise more questions than they answer. At some point, while researchers work on figuring out where the truth lies, it just makes sense to say the potential benefit outweighs the cost.
　　The best evidence to date concerns folate, one of the B vitamins. It's been proved to limit the number of defects in embryos (胚胎), and a recent trial found that folate in combination with vitamin B 12 and a form of B6 also decreases the re-blockage of arteries after surgical repair.
　　The news on vitamin E has been more mixed. Healthy folks who take 400 international units daily for at least two years appear somewhat less likely to develop heart disease. But when doctors give vitamin E to patients who already have he art disease, the vitamin doesn't seem to help. It may turn out that vitamin E plays a role in prevention but cannot undo serious damage.
　　Despite vitamin C's great popularity, consuming large amounts of it still has not been positively linked to any great benefit. The body quickly becomes saturated with C and simply excretes (排泄) any excess.
　　The multivitamins question boils down to this: Do you need to wait until all the evidence is in before you take them, or are you willing to accept that there's enough evidence that they don't hurt and could help?
　　If the latter, there's no need to go to extremes and buy the biggest horse pills or the most expensive bottles. Large doses can cause trouble, including excessive bleeding and nervous system problems.
　　Multivitamins are no substitute for exercise and a balanced diet, of course.
　　As long as you understand that any potential benefit is modest and subject to further refinement, taking a daily multivitamin makes a lot of sense.ce you've got to work hard.

　　Some futurologists have assumed that the vast upsurge (剧增) of women in the workforce may portend a rejection of marriage. Many women, according to this hypothesis, would rather work than marry. The converse (反面) of this concern is that the prospects of becoming a multi-paycheck household could encourage marriages. In the past, only the earnings and financial prospects of the man counted in the marriage decision. Now, however, the earning ability of a woman can make her more attractive as a marriage partner. Data show that economic downturns tend to postpone marriage because the parties cannot afford to establish a family or are concerned about rainy days ahead. As the economy rebounds, the number of marriages also rises.
　　Coincident with the increase in women working outside the home is the increase in divorce rates. Yet, it may be wrong to jump to any simple cause-and-effect conclusions. The impact of a wife’s work on divorce is no less cloudy than its impact on marriage decisions. The realization that she can be a good provider may increase the chances that a working wife will choose divorce over an unsatisfactory marriage. But the reverse is equally plausible. Tensions grounded in financial problems often play a key role in ending a marriage. Given high unemployment, inflationary problems, and slow growth in real earnings, a working wife can increase household income and relieve some of these pressing financial burdens. By raising a family’s standard of living, a working wife may strengthen her family’s financial and emotional stability.
　　Psychological factors also should be considered. For example, a wife blocked from a career outside the home may feel caged in the house. She may view her only choice as seeking a divorce.
　　On the other hand, if she can find fulfillment through work outside the home, work and marriage can go together to create a stronger and more stable union.
　　Also, a major part of women’s inequality in marriage has been due to the fact that, in most cases, men have remained the main breadwinners. With higher earning capacity and status occupations outside of the home comes the capacity to exercise power within the family. A working wife may rob a husband of being the master of the house. Depending upon how the couple reacts to these new conditions, it could create a stronger equal partnership or it could create new insecurities.

　　For most thinkers since the Greek philosophers, it was self-evident that the re is something called human nature, something that constitutes the essence of man. There were various views about what constitutes it, but there was agreement that such an essence exists—that is to say, that there is something by virtue of which man is man. Thus man was defined as a rational being, as a social animal, an animal that can make tools, or a symbol-making animal.
　　More recently, this traditional view has begun to be questioned. One reason for this change was the increasing emphasis given to the historical approach to man. An examination of the history of humanity suggested that man in our epoch is so different from man in previous times that it seemed unrealistic to assume that men in every age have had in common something that can be called “human nature.” The historical approach was reinforced, particularly in the United States, by studies in the field of cultural anthropology (人类学). The study of primitive peoples has discovered such a diversity of customs, values, feelings, and thoughts that many anthropologists arrived at the concept that man is born as a blank sheet of paper on which each culture writes its text. Another factor contributing to the tendency to deny the assumption of a fixed human nature was that the concept has so often been abused as a shield behind which the most inhuman acts are committed. In the name of human nature, for example, Aristotle and most thinkers up to the eighteenth century defended slavery. Or in order to prove the rationality and necessity of the capitalist form of society, scholars have tried to make a case for acquisitiveness, competitiveness, and selfishness as innate (天生的) human traits. Popularly, one refers cynically to “human nature” in accepting the inevitability of such undesirable human behavior as greed, murder, cheating and lying.
　　Another reason for skepticism about the concept of human nature probably lies in the influence of evolutionary thinking. Once man came to be seen as developing in the process of evolution, the idea of a substance which is contained in his essence seemed untenable. Yet I believe it is precisely from an evolutionary standpoint that we can expect new insight into the problem of the nature of man.

　　Richard Satava, program manager for advanced medical technologies, has been a driving force in bringing virtual reality to medicine, where computers create a “virtual” or simulated environment for surgeons and other medical practitioners (从业者).
　　“With virtual reality we’ll be able to put a surgeon in every trench,” said Satava. He envisaged a time when soldiers who are wounded fighting overseas are put in mobile surgical units equipped with computers.
　　The computers would transmit images of the soldiers to surgeons back in the U.S. The surgeons would look at the soldier through virtual reality helmets (头盔) that contain a small screen displaying the image of the wound. The doctors would guide robotic instruments in the battlefield mobile surgical unit that operate on the soldier.
　　Although Satava’s vision may be years away from standard operating procedure, scientists are progressing toward virtual reality surgery. Engineers at an international organization in California are developing a tele-operating device. As surgeons watch a three-dimensional image of the surgery, they move instruments that are connected to a computer, which passes their movements to robotic instruments that perform the surgery. The computer provides feedback to the surgeon on force, textures, and sound.
　　These technological wonders may not yet be part of the community hospital setting but increasingly some of the machinery is finding its way into civilian medicine. At Wayne State University Medical School, surgeon Lucia Zamorano takes images of the brain from computerized scans and uses a computer program to produce a 3-D image. She can then maneuver the 3-D image on the computer screen to map the shortest, least invasive surgical path to the tumor (肿瘤). Zamorano is also using technology that attaches a probe to surgical instruments so that she can track their positions. While cutting away a tumor deep in the brain, she watches the movement of her surgical tools in a computer graphics image of the patient’s brain taken before surgery.
　　During these procedures—operations that are done through small cuts in the body in which a miniature camera and surgical tools are maneuvered—surgeons are wearing 3-D glasses for a better view. And they are commanding robot surgeons to cut away tissue more accurately than human surgeons can.
　　Satava says, “We are in the midst of a fundamental change in the field of medicine.”

    Thomas Malthus published his “Essay on the Principle of Population” almost 200 years ago. Ever since then, forecasters have being warning that worldwide famine was (S1) just around the next corner. The fast-growing population’s demand for food, they warned, would soon exceed their (S2) supply, leading to widespread food shortages and starvation.
    But in reality, the world’s total grain harvest has risen steadily over the years. Except for relative isolated trouble (S3) spots like present-day Somalia , and occasional years of good harvests, the world’s food crisis has remained just (S4) around the corner. Most experts believe this can continue even as if the population doubles by the mid-21st century, (S5) although feeding 10 billion people will not be easy for politics, economic and environmental reasons. Optimists (S6) point to concrete examples of continued improvements in yield. In Africa, by instance, improved seed, more (S7) fertilizer and advanced growing practices have more than double corn and wheat yields in an experiment. Elsewhere, (S8)rice experts in the Philippines are producing a plant with few (S9) stems and more seeds. There is no guarantee that plant breeders can continue to develop new, higher-yielding crop, but most researchers see their success to date as reason (S10) for hope.

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