[A]That world is not yet on offer. But a semblance of it might be one day. Senescence:, the general dwindling of prowess experie

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问题    [A]That world is not yet on offer. But a semblance of it might be one day. Senescence:, the general dwindling of prowess experienced by all as time takes its toll, is coming under scrutiny from doctors and biologists. Suspending it is not yet on the cards. But slowing it probably is. Average lifespans have risen a lot over the past century, but that was thanks to better food, housing, public health and some medicines. This, optimists claim, will extend life for many people to today’s ceiling of 120 or so. But it may be just the beginning. In the next phase not just average lifespans but maximum lifespans will rise. If a body part wears out, it will be repaired or replaced altogether. DNA will be optimised for long life. Add in anti-ageing drugs, and centenarians will become two a penny.
   [B]One concern is that long life will exacerbate existing social and economic problems. The most challenge will be access to anti-senescence treatment. If longer life is expensive, who gets it first? Already, income is one of the best predictors of lifespan. Widening the gap with treatments inaccessible to the poor might deepen divisions that are already straining democracies.
   [C]Imagine as a world in which getting fitted with a new heart, liver or set of kidneys, all known from your own body cells, was as commonplace as knee and hip replacements are now. Or one in which you celebrated your 94th birthday by running a marathon with your school friends. Imagine, in other words, a world in which ageing had been abolished.
   [D]Longevity is known to run in families, which suggests that particular varieties of genes prolong life. Some are investigating this, with the thought that modern gene-editing techniques might one day be used to make crucial, life-extending tweaks to the DNA of those who need them. From an individual’ s viewpoint, this all sounds very desirable. From society as a whole, though, it will have profound effects. Most of them will be good, but not all.
   [E]Such speculation is fun, and mostly optimistic. The promise of a longer life, well lived, would round a person out. But this vision of the future depends on one thing — that a long existence is also a healthy one. Humanity must avoid the trap fallen into by Tithonus, a mythical Trojan who was granted eternal life by the gods, but forgot to ask also for eternal youth. Eventually, he withered into a cicada.
   [F]Will older workers be discriminated against, as now, or will numbers give them the whip hand over the young? Will bosses cling on, hampering the careers of their underlings, or will they grow bored, quit and do something else entirely? And would all those old people cease to consider themselves elderly, retaining youthfully vigorous mental attitudes as well as physical ones —or instead make society more conservative (because old people tend to be)?[G]To this end, many hopeful repairmen are now setting up shop. Some of them want to upgrade worn-out tissues using stem cells (precursors to other sorts of cell). Such bio-renovation is the basis of an unproven, almost vampiric, treatment in vogue in some circles: transfusion into the old of the blood of the young. The business of growing organs from scratch is also proceeding. At the moment, these "organoids" are small, imperfect and used mainly for drug testing. But that will surely change.
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答案B

解析 本题需要确定第五段。通过分析B、F两个备选项可知,浏览发现F段都是问句, 而B段反复出现的表达是long life,longer life,lifespan等,说明B段是在探讨长寿的问题, 可以与上一段紧密衔接,故选B。
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