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Almost everybody wants to live as long as possible. And given the enormous strides made in medicine and the health sciences duri

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问题    Almost everybody wants to live as long as possible. And given the enormous strides made in medicine and the health sciences during the past 150 years, people could be forgiven for hoping that someday human beings will live, if not quite forever, at least far longer than at present. Since the mid 19th century, average life expectancy at birth has nearly doubled: from 40 years to 75. Today many people live past 100, and the oldest individuals have reached either 115 or 120, depending on whom you believe.
   So it comes as something of a surprise to be told by the experts that human beings have taken life about as far as it can go. That is the serious conclusion of a report in Science magazine last week by S. Jay Olshansky and Christine Cassel. Unless an unexpected breakthrough in basic science that would prevent the aging process, the era of rapid increases in human life span has come to an end, at least in developed countries. Even if science could cure heart disease and cancer, which account for nearly 50 percent of all deaths in the U. S. , it is unlikely that the average life expectancy at birth would increase much beyond 85.
   What makes the report so compelling is that it is based on simple mathematics. In the past, the upper limits of life have been guessed from actuarial tables by estimating how death rates would change if, say, the incidence of heart disease were halved. "We reversed the question," says Olshan sky. Taking an" engineering approach" his team members asked themselves how many death rates would have to be reduced in order to increase average life expectancy to 120 years. What they discovered, after running the numbers through a computer, was that big hits in current death rates in the U. S. would give only small lifts to life expectancy. For example, if some miracle of medicine can guarantee no one died before reaching age 50 (thus eliminating 12 percent of all deaths), the increase in average life expectancy would be only 3.5 years.
   There seems to be a kind of built-in biological limit programmed into the cells of the human body. In laboratory experiments, human cells divide only about 50 times before they begin to fall apart like old cars. This planned loss of use on nature’s part makes a certain amount of evolutionary sense. Survival of the fittest, after all, rewards only those who reproduce, not necessarily those who reach old age, Once reproduction is over, human bodies may as well be throwaway goods, biologically speaking.
What can we infer from the text?
选项 A、It is easy to prolong the average life span in developed country, because of the advanced health science.
B、It is difficult to prolong the average life span greatly, because science cannot prevent the aging process now.
C、If the diseases that cause most of the death can be cured, the average life span will increase greatly.
D、More and more people will live past 100 if the diseases that cause most of the death can be cured.
答案B
解析 纵观全文，文章主要说明的是尽管科学和医疗的进步使人类的寿命越来越长，但是如果科学在阻止人类衰老方面没有突破的话，人类的平均寿命是不可能有大幅度延长的。A与文意不符，对于发达国家来说延长人类的平均寿命也不是容易的事。C与文意不符，即使主要导致人类死亡的疾病能够被治愈，人类的平均寿命会有小幅度而不是大幅度延长。D文章未提及这两者的联系。
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