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专限时训练(二十三) [资讯报道型阅读理解] (限时：每篇7分钟) (一) MIT researchers and their colleagues are working to find out whether energy from trees can power a network of sensors (传感器) to prevent spreading forest fires. What they learn could also raise the possibility of using trees as silent guards along the nation’s borders to discover potential threats such as smuggled (走私的) radioactive materials. The U．S. Forest Service currently predicts and tracks fires with a variety of tools, including remote automatic weather stations. But these stations are expensive and sparsely (稀疏地) distributed. Additional sensors could save trees by providing better local climate data to be used in fire prediction models and earlier warnings. However, recharging or replacing batteries by hand at very hardtoreach locations makes it impractical and costly. The new sensor system seeks to avoid this problem by developing trees into a selfsustaining power supply. Each sensor is equipped with a battery that can be slowly recharged using electricity produced by the tree. “A single tree doesn’t generate a lot of power, but over time the trickle (细流) charge adds up, just like ________” said Shuguang Zhang, one of the researchers on the project and the associate director of the MIT’s Center for Biomedical Engineering (CBE)． | 
