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 WoodsHole, 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 just make sure to look both ways before crossing the street!
单选题
Backpacks are convenient because ______. A. they can be very large B. they can hold as many things as you want to carry C. your hands are freed to do other things D. you do not have to carry things with you
【正确答案】
C
【答案解析】第一段告诉我们，因为背包可以装许多东西，所以可以将双手解放出来做其他事情：to free your hands to do other things。
单选题
What is the most important feature of the backpack invented by Lawrence C. Rome and his colleagues? A. It produces electricity for electronic devices while the wearer walks. B. It can be used as cell phones, GPS in the military actions or field studies. C. It is small and convenient. D. It is light and easy to carry.
【正确答案】
A
【答案解析】第二段的第一句说，Lawrence C. Rome及其同事们发明的这种背包，当背看背包走路时，会有电能产生；该段最后一句告诉我们，背包的这种性能可减少背包的重量，因为不必携带备用电池。
单选题
The word "springs" in Paragraph 3 means ______. A. a small stream of water flowing naturally from the earth B. the season of the year, occurring between winter and summer C. the act or an instance of jumping or leaping D. a length of metal wound around, which returns to its original shape after being pushed
单选题
According to Paragraph 4, what does Rome plan to do? A. To make the backpack more comfortable for the wearer. B. To put the backpack on the market. C. To test the advantage of the backpack. D. To promote the backpack in a newspaper or on television.
单选题
What is implied in "if you do get one eventually, just make sure to look both ways before crossing the street!"? A. You will be too excited to watch the traffic. B. Enjoying electronic devices while walking may invite traffic accidents. C. It is not possible for you to get such a backpack. D. It is wise of you to have such a backpack.