Clever genetic detective work may have found out the reason why a near-starvation diet prolongs the life of many animals. Ronald Kahn at Harvard Medical School in Boston, US, and his colleagues have been able to extend the lifespan (寿命) of mice by 18 percent by blocking the rodent's (啮齿动物) increase of fat in specific cells. This suggests that thinness-and not necessarily diet-promotes long life in "calorie (热量单位，卡) restricted" animals. "It's very cool work," says aging researcher Cynthia Kenyon of the University of California, San Francisco. "These mice eat all they want, lose weight and live longer. It's like heaven. " Calorie restriction dramatically extends the lifespan of organisms as different as worms and rodents. Whether this works in humans is still unknown, partly because few people are willing to submit to such a strict diet. But many researchers hope they will be able to trigger the same effect with a drug once they understand how less food leads to a longer life. One theory is that eating less reduces the increase of harmful things that can damage cells. But Kahn's team wondered whether the animals simply benefit by becoming thin. To find out, they used biology tricks to disrupt the insulin (胰岛素) receptor (受体) gene in lab mice—but only in their fat cells. "Since insulin is needed to help fat cells store fat, these animals were protected against becoming fat," explains Kahn. This slight genetic change in a single tissue had dramatic effects. By three months of age, Kahn's modified mice had up to 70 percent less body fat than normal control mice, despite the fact that they ate 55 percent more food per gram of body weight. In addition, their lifespan increased. The average control mouse lived 753 days, while the thin rodents averaged a lifespan of 887 days. After three years, all the control mice had died, but one-quarter of the modified rodents were still alive. "That they get these effects by just manipulating the fat cells is controversial, "says Leonard Guarente of the Massachusetts Institute of Technology, who studies calorie restriction and aging. But Guarente says Kahn has yet to prove that the same effect is responsible for increased lifespan in calorie restricted animals. "It might be the same effect or there might be two routes to long life," he points out, "and that would be very interesting./
单选题
Ronald Kahn and his colleagues can make mice live longer by ______. A. offering them less food B. giving them a balanced diet C. disrupting the specific genes in their fat cells D. preventing them growing larger
【正确答案】
C
【答案解析】[解析] 这里的定位词可以是Ronald Kahn and his colleagues和mice，在原文第二段中找到相关句：“Ronald Kahn at Harvard Medical School in Boston, US, and his colleagues have been able to extend the lifespan of mice by 18 percent by blocking the rodent's increase of fat in specific cells.”，其中“extend the lifespan of mice”是“延长老鼠寿命”的意思。这里的“by blocking the rodent's...”是by引导的方式状语从句。这里的“fat in specific ceils”恰好对应了选项C的specific genes in their fat cells，故选C。
单选题
According to the passage, we do not know whether humans will benefit from taking in fewer calories partly because ______. A. humans, worms and rodents are different B. most people are not willing to be put on a strict diet C. the effect is not known D. genetic changes in tissues can not be performed on humans
【正确答案】
B
【答案解析】[解析] 关于human的叙述在第四段第二句：“Whether this works in humans is still unknown, partly because few people are willing to submit to such a strict diet.”所以选B。
单选题
What does the last sentence in the third paragraph imply? A. People like to lose weight, but they do not like to eat less. B. People want to go to heaven, but they do not want to die. C. Mice will go to heaven if they lose weight. D. Mice enjoy losing weight.
【正确答案】
A
【答案解析】[解析] 可以在第三段中找到相应句子，“These mice eat all they want, lose weight and live longer. It's like heaven.”(这些老鼠们吃它们想吃的，还减肥并且还长寿，这简直就是天堂!)将选项翻译出来，发现只有A合适。这句话的言外之意就是人们减肥但是又不想少吃。所以mice的这种情况被认为是天堂。
单选题
The average modified mouse lived ______. A. 3 years B. 753 days C. more than 3 years D. 887 days
【正确答案】
D
【答案解析】[解析] 关键词是average modified mouse，在原文倒数第三段第二句找到“The average control mouse lived 753 days, while the thin rodents averaged a lifespan of 887 days.”这里经改良的mouse就是指比较瘦的，所以这里选D项。
单选题
What can be inferred from the passage about the route to long life? A. It remains to be studied. B. It has already been discovered. C. Eating more leads to long life. D. Eating less leads to long life.
【正确答案】
A
【答案解析】[解析] 关于走向长寿的路径，属于总结性的问题，在最后一段第二句中“'It might be the same effect or there might be two routes to long life,' he points out, 'and that would be very interesting.'”这里作者在effect和routes前都用了might一词，说明还不确定这种效果能不能在人身上体现，所以选项A比较符合题意，故选A。