单选题Of the reptile groups, the snake group was the final one to appear.A. lastB. bestC. ugliestD. longest

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, U.S., 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 not 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"s 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The river Uwidens/U considerably as it begins to turn east.

单选题It was hard to say why the man deserved such {{U}}shabby{{/U}} treatment. A. unforgettable B. unbelievable C. unfair D. unthinkable

单选题We have abundant evidence to prove his guilt.

单选题We"re happy to report that business is booming this year.

单选题Today's film makers emphasize special effects at the expense of the story.

单选题The manchineel tree has smooth, pale brown bark and long, {{U}}drooping{{/U}} branches.

单选题They decided to abandon the saving plan after discussion.A. give outB. give upC. give inD. give off

单选题The chairman Uproposed/U that we stop the meeting.

单选题Acknowledged as the main cause of hay fever the pollen of ragweed is very bothersome .

单选题What are my chances of promotion if I stay here?A. retirementB. replacementC. advertisementD. advancement

单选题When doves are about two weeks old, they are covered with grey feathers and are ready to try their wings.A. growB. wrapC. hideD. test

单选题Electric Backpack Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hands free to do other things. Someday, if you don't mind carrying a heavy load, your backpacks might also power your MP3 player, keep your cell phone running, and maybe even light your way home. Lawrence C. Rome and his colleagues from the University of Pennsylvania in Philadelphia and the Marine Biological Laboratory in Woods Hole, Mass, have invented a backpack that makes electricity from energy produced while its wearer walks. In military actions, search-and-rescue operations, and scientific field studies, people rely increasingly on cell phones, global positioning system (GPS) receivers, night-vision goggles, and other battery-powered devices to get around and do their work. The backpack's electricity-generating feature could dramatically reduce the amount of a wearer's load now devoted to spare batteries, report Rome and his colleagues in the Sept. 9, Science. The backpack's electricity-creating powers depend on springs used to hang a cloth pack from its metal frame. The frame sits against the wearer's back, and the whole pack moves up and down as the person walks. A gear mechanism converts vertical movements of the pack to rotary motions of an electrical generator, producing up to 7.4 watts. Unexpectedly, tests showed that wearers of the new backpack alter their gaits in response to the pack's oscillations, so that they carry loads more comfortably and with less effort than they do ordinary backpacks. Because of that surprising advantage, Rome plans to commercialize both electric and non-electric versions of the backpack. The backpack could be especially useful for soldiers, scientists, mountaineers, and emergency workers who typically carry heavy backpacks. For the rest of us, power-generating backpacks could make it possible to walk, play video games, watch TV, and listen to music, all at the same time. Electricity-generating packs aren't on the market yet, but if you do get one eventually, ~ust make sure to look both ways before crossing the street!

单选题It might be more prudent to get a second opinion before going ahead.

单选题The latest car model Uembodies/U many new improvements.

单选题Our New York branch is dealing with the matter. ______

单选题weather is a constant (subject) of conversation inBritain.

单选题Data Insecurity It never rains but it pours. Just as bosses and boards have finally sorted out their worst accounting and compliance troubles, and improved their feeble corporation governance, a new problem threatens to earn them, especially in America, the sort of nasty headlines that inevitably lead to heads rolling in the executive suite: data insecurity. Left, until now, to odd, low-level IT staff to put right, and seen as a concern only of data-rich industries such as banking, telecoms and air travel, information protection is now high on the boss"s agenda in businesses of every variety. Several massive leakages of customer and employee data this year—from organizations as diverse as Time Warner, the American defense contractor Science Applications International Corp and even the University of California, Berkeley have left managers hurriedly peering into their intricate IT systems and business processes in search of potential vulnerabilities. "Data is becoming an asset which needs to be guarded as much as any other asset," says Haim Mendelson of Stanford University"s business school. "The ability to guard customer data is the key to market value, which the board is responsible for on behalf of shareholders." Indeed, just as there is the concept of Generally Accepted Accounting Principles (GAAP), perhaps it is time for GASP, Generally Accepted Security Practices, suggested Eli Noam of New York"s Columbia Business School. "Setting the proper investment level for security, redundancy, and recovery is a management issue, not a technical one," he says. The mystery is that this should come as a surprise to any boss. Surely it should be obvious to the dimmest executive that trust, that most valuable of economic assets, is easily destroyed and hugely expensive to restore and that few things are more likely to destroy trust than a company letting sensitive personal data get into the wrong hands. The current state of affairs may have been encouraged, though not justified by the lack of legal penalty (in America, but not Europe) for data leakage. Until California recently passed a law, American firms did not have to tell anyone, even the victim, when data went a-stray. That may change fast: lots of proposed data-security legislation is now doing the rounds in Washington, D.C. Meanwhile, the theft of information about some 40 million credit-card accounts in America, disclosed on June 17th, overshadowed a hugely important decision a day earlier by America"s Federal Trade Commission (FFC) that puts corporate America on notice that regulators will act if firms fail to provide adequate data security.

单选题The Constitution's vague nature has given it the flexibility to be adapted when circumstances change.A. impreciseB. conciseC. unpolishedD. elementary