理工类C级：阅读理解ElectricBackpack
Backpacks are convenient. They can hold your books，your lunch，and achange of clothes，leaving your hands free to do other things.Someday，if youdont mind carrying a heavy load，your backpacks might also power your MP31player，keep your cell phone running，and maybe even light your wayhome.
Lawrence C. Rome and his colleagues from the University of Pennsylvania in Philadelphia2 and the Marine Biological Laboratory in WoodsHole3，Mass.4，have invented a backpack that makes electricity from energyproduced while its wearer walks. In military actions，search-and-rescueoperations，and scientific field studies，people rely increasingly on cellphones，global positioning system (GPS) 5 receivers，night-vision goggles，andother battery powered devices to get around and do their work. The backpackselectricity- generating feature could dramatically reduce the amount of awearers load now devoted to spare batteries，report Rome and his colleagues inthe Sept.9 Science6.
The backpacks electricity-creating powers depend onsprings used to hang a cloth pack from its metal frame.The frame sits againstthe wearers back，and the whole pack moves up and down as the person walks.Agear mechanism converts vertical movements of the pack to rotary motions of anelectrical generator，producing up to 7.4 watts.
Unexpectedly，tests showedthat wearers of the new backpack alter their gaits in response to the packsoscillations，so that they carry loads more comfortably and with less effortthan they do ordinary backpacks. Because of that surprising advantage，Rome plans to commercialize both electric and non-electric versionsof the backpack.
The backpack could be especially useful forsoldiers，scientists，mountaineers，and emergency workers who typically carryheavy backpacks.For the rest of us，power-generating backpacks could make itpossible to walk，play video games，watch TV，and listen to music，all at the sametime.Electricity-generating packs arent on the market yet，but if you do get one eventually，just make sure to look both ways before crossing thestreet！
1. Backpacks are convenient because
A they can be verylarge.
B they can hold as many things as you want to carry.
C your handsare freed to do other things.
D you do not have to carry things withyou.
2. What is the most important feature of the backpack invented byLawrence C.Rome
and his colleagues?
A It produces electricity forelectronic devices while the wearer walks.
B It can be used as cellphones，GPS in the military actions or field studies.
C It is small andconvenient.
D It is light and easy to carry.
3. The word "springs" inParagraph 3 means
A a small stream of water flowing naturally from theearth.
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 woundaround，which returns to its original shape after
being pushed.