单选题
Eat More, Weigh Less, Live Longer

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 per cent by blocking the rodent's (啮齿动物) increase of fat in specific cells. This suggests that thinness—and hot necessarily diet—promotes long life in "calorie (热量卡) 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, those modified mice had up to 70 per cent less body fat than normal control mice, despite the fact that they ate 55 per cent 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] 细节题。利用题干关键词Ronald Kahn和live longer可定位到第二段“Ronald Kahn and his colleagues have been able to extend the lifespan of mice by 18 percent by blocking the rodent's (啮齿动物) increase of fat in specific cells”，即“Ronald Kahn和他的同事能延长老鼠的寿命达18%，通过阻止特定细胞中脂肪的增长”，故C为正确答案。
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] 细节题。利用题干关键词可以定位到第四段“Whether this works in humans is still unknown, partly because few people are willing to submit to such a strict diet”，即“是否这也对人起作用还未可知，部分地因为几乎没有人愿意接受这样严格的饮食安排”，所以B为正确答案。
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] 推断题。第三段的最后一个句子是“these mice eat all they want, lose weight and live longer. It's like heaven”，即“这些老鼠可以敞开吃，不会发胖，还能长寿。这就像进入天堂一样”。这实际上是道出了人的心声，由此答案为A。
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] 细节题。利用题目关键词safety和manufacturing company等可以定位到倒数第二段“The average control mouse lived 753 days, while the thin rodents averaged a lifespan of 887 days”，即“在普通监控下的老鼠活了753天，而那些瘦的平均寿命则达到887天”，所以正确答案为D。
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] 推断题。从文章的最后两段我们可以感到对Kahn的试验，同行中是有不同意见的，至少到目前为止还不能说已经找到了延长寿命的方法，由此推断答案为A。