Themountingevidencefor age genes that influence the agingprocessis by no meansconclusive, but it is quiteimpressive, coming from avarietyofindependentresearch from aging in worms and fruit flies to antioxidants andgenerepair mechanisms, and human mutations. Still, the connections are circumstantial.

Christopher Wills, professor ofbiologyat the University of California in San Diego, thinks that by 2025 science will likelyisolatethemammalianage genes inmice. We shareroughly75 percent of our genes withmiceand have much the same body chemistry; this is a strongreasonto believe that an agegenefound inmicecould also be at work in humans. If such genes are located, the next step would be to find out if these age genes have their counterparts in humans. Wills believes that if they are found in humans, they mayextendthe human lifespanperhaps to 150 years.

But by 2020, when personalized DNA sequencing becomeswidespread, asecondtacticmay prove fruitful as well. By analyzing populations of healthy individuals in their nineties and beyond, scientists will find it possible to use computers tocomparetheirgeneticbackgrounds and cross-check for similarities in key genes that are suspected of influencing aging. Acombinationof studies on the DNA of long-lived animals and on the personalized DNA sequences of elderly individuals mayconsiderablynarrow down the search for the agegene.

As yet, none of these methods can prove that we can increase the human lifespan. Indeed, the onlytheorywith a proventrackrecordof extending the lifespanof animals is the caloric restrictiontheory, which states that animals whichconsumecalories just abovestarvationlevels livesignificantlylonger than theaverage. Although thistheoryflies in the face ofcommonsense(a well-fed animal is well nourished and healthy, and should have greaterresistancetodiseaseand aging), it has held up under repeated testing among a wide range of animals. Scientists haveconsistentlyincreased the lifespanof rats andmicein thelaboratoryby 50 to 100 percent. It is the only laboratory-testedtheoryof ageextensionfor animals that has held up under decades of carefulscrutiny. Why?

Acrossthe animalkingdom, the lifespanof animals isroughlyinversely correlated to themetabolismrate. The slower their normalmetabolismrate, the longer their normal lifespan. In 1996, in a study that reduced thecalorieintake of 200 monkeys by 30 percent, the monkeys were shown to have a slowermetabolismrate, a longer lifespan, and reduced rates of cancer, heartdisease, anddiabetes. “We have known for 70 years that if you feedlaboratorymiceless food, they age slower, they live longer, and they get diseases less frequently. We find that monkeysrespondin the same way as rodents and that the same biological changes may be in play here,” says George Roth of the NationalInstituteof Aging.

There is still room forscientificdebateon the question “why?” Ron Hart, a scientist at the National Center for Toxicological Research, believes that the answer may tie in the high bodytemperatureof mammals, and humans inparticular. “Heat causes pieces of the DNAmoleculetosplitoff randomly, and it must be repaired,” Hart says. “Undercalorierestriction, though, theengineruns cooler and there’s less damage. Merely reducing caloric intake by 40 percent reduced this form ofspontaneousDNA damage almost 24 percent!” Furthermore, at a higherinternalbodytemperature,oxygenis being burned at a greaterrate, creating more free radicals, which also speed up the agingprocess. Cooling the body, on the other hand, increases theamountof antioxidants in the body. Hart found a fourfold increase in theenzymecatalase and a threefold increase insuperoxidedismutasein animals on arestricteddiet. “What’sfascinating," Hart concludes, “is that reduced food intake is the onlyexperimentalparadigm ever found that enhances DNA repair.” Hart is so convinced of the importance of this work that in 1993 he began the firstsystematicstudies of caloric restrictions in humans.

Questions:
question_stem: The word “conclusive”in the passage is closest in meaning to
choices: tag: A
text: clear

tag: B
text: independent

tag: C
text: usual

tag: D
text: final
answer_key: D
explanation: conclusive 解释为“最后的，确定性的，结论性的”；A 清楚的；B 独立的；C 通常的；D 最后的；所以答案选 D。

question_stem: According to paragraph 1, evidence for age genes has come from research into each of the following EXCEPT
choices: tag: A
text: mutations in humans

tag: B
text: aging in fruit flies

tag: C
text: connections among various genes

tag: D
text: the process by which damaged genes get repaired
answer_key: C
explanation: 题干问：关于衰老基因的证据不是来源于以下哪些研究？
“A 人类基因突变 B 果蝇的衰老 C 损坏基因修复的过程” 都对应到第一段第一句话中“coming from a variety of independent research from aging in worms and fruit flies to antioxidants and gene repair mechanisms, and human mutations ” C 文中未提到。

question_stem: According to paragraph 2, success at isolating age genes in mice would provide support for the idea that
choices: tag: A
text: mice and humans have very similar body chemistry

tag: B
text: mice and humans have about 75 percent of their genes in common

tag: C
text: aging in mice occurs more rapidly than aging in humans does

tag: D
text: age genes are likely to be found in humans
answer_key: D
explanation: 题干问：成功分离老鼠中的衰老基因可以支持一下哪个观点？根据定位词 isolating age genes in mice 定位到第2、3句话：我们和老鼠大约有75%的基因相同，身体化学成分也基本相同;这是一个有力的理由让我们相信在老鼠身上发现的衰老基因可能也在人类身上起作用。如果找到了这些基因，下一步将是找出这些衰老基因在人类中是否有对应的基因。D 符合；A 和 B 有提到，但不是分离基因所得出的结论；C 文中未提到；

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Although the caloric restriction theory is widely accepted, it is the only theory about extending the life span of animals that has not yet been fully proven.

tag: B
text: Research has shown that limiting calorie intake to just above the level needed to survive can increase life expectancy.

tag: C
text: Only the caloric restriction theory analyzes the calorie consumption of animals with both average and extended life spans.

tag: D
text: Records over the life spans of animals indicate that starvation levels are rare when calories are restricted.
answer_key: B
explanation: 原句大致释义为：事实上，唯一有证据证明可以延长动物寿命的理论是热量限制理论，该理论指出，摄入热量仅略高于饥饿水平的动物寿命明显长于平均水平。A 中的转折原句未体现，无中生有；C“只有热量限制理论分析平均寿命和延长寿命的动物的热量消耗”改写了原句的意思，“只有热量限制理论分析…“和原句的” 唯一有证据证明可以延长动物寿命的理论是热量限制理论“不符合；D 大致意思为“动物寿命的记录表明，当热量受到限制时，饥饿水平是很少见的”，原句核心意思完全没提到饥饿水平这一点；B 大致意思为：研究表明，将卡路里摄入量限制在略高于生存所需的水平可以延长寿命，符合原句意思。

question_stem: The word “scrutiny”in the passage is closest in meaning to
choices: tag: A
text: planning

tag: B
text: repetition

tag: C
text: examination

tag: D
text: Emphasis
answer_key: C
explanation: scrutiny 监视、详细检查；A 计划;  B 重复、反复；D 强调、重点；C 检查、查问，符合意思只有 C。

question_stem: What purpose does paragraph 5 serve in the larger discussion of research into age- related genes?
choices: tag: A
text: To explain why the caloric restriction theory has remained believable over the years

tag: B
text: To explain why the caloric restriction theory was the only theory of age extension that was tested in laboratories

tag: C
text: To explain the process involved in extending the life span of animals

tag: D
text: To explain the length of time that research into life span extension has been going on
answer_key: A
explanation: 但是题干问的是第五段在讨论衰老基因相关的研究中起到什么样的目的？需要阅读理解整个段落，并梳理段落的主旨中心并且结合上下文进行解答；该段一开始指出新陈代谢与寿命的负相关性，然后用实验表明摄入热量少，新陈代谢慢，寿命可能越长；由此与上一段的内容有关系，上一段内容主要在介绍热量限制理论，即适当控制热量摄入有助于寿命延长；故而，这段与上一段的关系主要就是本段进一步解释并支持了热量限制理论。故而答案选 A。B 中的“唯一的在实验室里进行验证的理论”这一点不符合原文意思；C 中提到的延长寿命的过程不符合；D 强调的是寿命延长的研究所做的时间长度，不符合。

question_stem: The discussion in paragraph 6 of Hart’s theory suggests that
choices: tag: A
text: free radicals have a negative influence on the life span of mammals

tag: B
text: antioxidants tend to lower the body temperature of some mammals but not others

tag: C
text: calorie restriction generally decreases enzyme activity

tag: D
text: the high body temperature of mammals reduces the need for further calorie consumption
answer_key: A
explanation: 哈特（Hart）的理论暗示了什么？结合本段 Hart 的理论，理论指出：身体温度越高，基因损害越严重，修复也越多；此外体温越高，产生的自由基越多，越容易加速衰老；故而控制热量摄入，可以降低体温，从而减缓衰老；还有，身体温度降低，抗氧化剂增加，有助于防止衰老；A 选项符合，自由基对哺乳动物的寿命有负面影响；B “抗氧化剂可以降低一些哺乳动物的体温”与原文意思相反，应是体温降低，抗氧化剂增加；C 与原文意思相反，控制热量摄入可以增加酶；D 文章未提到，无中生有；

question_stem: According to paragraph 6, Hart maintains that extending the life span of mammals can be achieved by
choices: tag: A
text: increasing the amount of oxygen burned

tag: B
text: reducing internal body temperature

tag: C
text: improving the quality of free radicals in the body

tag: D
text: increasing the frequency of division in DNA molecules
answer_key: B
explanation: 题干问：哈特认为，延长哺乳动物的寿命可以通过以下方法来实现？结合本段 Hart 的理论，理论指出：身体温度越高，基因损害越严重，修复也越多；此外体温越高，产生的自由基越多，越容易加速衰老；故而控制热量摄入，可以降低体温，从而减缓衰老；还有，身体温度降低，抗氧化剂增加，有助于防止衰老；A 不符合，与原文相反；B 符合，降低体温可以降低新陈代谢从而减缓衰老；C 与原文相反，自由基增加会加速衰老而非减缓；D 加速 DNA 的分离是体温高的表现，反而是有助于衰老，不符合；故而选 B。