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 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!
词汇:
backpack/5bAkpAk/n.背包 watt/wCt /n.瓦
receiver/ri5si:vE/n.接收机 gait/eit/n.步态，步法
night-visiongoggle 夜视镜 oscillation/7Csi5leiFEn/n.摆动
spring/spriN /n.弹簧 commercialize/kE5mE:FElaiz/v.商业化
vertical/5vE:tikEl /adj.垂直的 mountaineer/7maunti5niE/n.登山运动员
rotary/5rEutEri /adj.旋转的
练习：
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.、
4. According to Paragraph 4，what does Rome plan to do?
A To make the backpackmore 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 anewspaper or on television.
5. What is implied in if you do get oneeventually，just make sure to took both
ways before crossing the street!?
A You will be too excited to watch the traffic.
B Enjoyingelectronic devices while walking may invite traffic accidents.
C It is notpossible for you to get such a backpack.
D It is wise of you to have such abackpack.
参考答案：
1.C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：tofree your hands to do other things。
2.A第二段的第一句说，Lawrence C.Rome及其同事们发明的这种背包，当背着背包走路时，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。
3.D springs在此是弹簧的意思。spring是一个多义词：泉水、春天、弹跳。
4.B 第四段最后一句的意思是：Rome计划将这种背包商业化，即推向市场。A、C、D在文中均未提到。D的意思是为背包做广告。
5.B这个句子的字面意思是：如果你终于得到这样的背包，过马路时一定要两面都看看。也就是说，不要因为同时玩着游戏，听着音乐、看着电视，太专注以致不注意来往车辆了。