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 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 (接收器), night-vision goggles (夜视镜), and other battery-powered devices to get around and do their work. The backpack"s electricity-generating feature could greatly reduce the amount of a wearer"s load now devoted to spare batteries.
The backpack"s electricity-creating powers depend on
springs
used to hang a cloth pack from its metal frame. The whole pack moves up and down as the person walks. A special mechanism converts movements of the pack to electricity, which can be as much as 7.4 watts.
Unexpectedly, tests showed that wearers of the new backpack alter their gaits (步法) in response to the pack"s oscillations (摆动), 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 nonelectric versions of the backpack.
The backpack could be especially useful for soldiers, scientists, mountaineers (登山运动员), 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 very convenient because they can ______.
【正确答案】
C
【答案解析】[解析] 事实细节题。由第一段前两句“Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hands free to do other things.”可知，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。故选C。
单选题
What is special about the backpack invented by Rome and his colleagues?
【正确答案】
B
【答案解析】[解析] 事实细节题。第二段第一句“...invented a backpack that makes electricity from energy produced while its wearer walks”提到，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“The backpack"s electricity-generating feature could greatly reduce the amount of a wearer"s load now devoted to spare batteries.”告诉我们，背包可以发电的这种性能可减少背包的重量，因为不必携带备用电池。故选B。
单选题
The word "springs" in Paragraph 3 means ______.
【正确答案】
B
【答案解析】[解析] 词义猜测题。spring是一个多义词：弹跳(A)、弹簧(B)、春天(C)、泉水(D)。由springs后的句子“used to hang a cloth pack from its metal frame”可知，此处“springs”为一个物件，可以挂东西，所以“springs”在此是“弹簧”的意思。故选B。
单选题
According to Paragraph 4, Rome plans to ______.
【正确答案】
C
【答案解析】[解析] 事实细节题。根据第四段最后一句“Because of that surprising advantage, Rome plans to commercialize both electric and non-electric versions of the backpack”可知，因为背包优点多，很好用，Rome计划将两种版型的背包商业化，即推向市场。故选C。
单选题
The sentence "if you do get one eventually, just make sure to look both ways before crossing the street!" implies ______.