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生态系统指由生物群落与无机环境构成的统一整体。生态系统的范围可大可小，相互交错，最大的生态系统是生物圈。生态系统是开放系统，为了维系自身的稳定，生态系统需要不断输入能量，否则就有崩溃的危险。生态系统是生态学领域的一个主要结构和功能单位，属于生态学研究的最高层次。 下列各项中，构成生态系统的是( )。
Passage Five Californian Michael Schwabe said goodbye to the gas pump two years ago. He leased an electric car. Schwabe says he gets more out of driving an electric car than just a charge. "With the price of gasoline and with the problems with clean air, it’s important we get electric vehicles out on the road." On California roads there are about two thousand electric cars. By 2003, ten percent of all new cars may be required to have zero emissions. This is a mandate automakers say it is way ahead of its time. Gloria Bergquist of the Alliance of Auto Manufacturers says, "The technology (for zero emissions) isn’t here yet; it still needs advancement in driving range to make it more appealing to a wider consumer audience ." Automakers blame it on the batteries. Power runs out on most cars after about 70 miles. However, some cars can now go more than 100 miles on a charge. Batteries are expensive. Carmakers say there is nothing they can do about it. Tim Carmichael of the Clean Air Coalition says, "The automakers have not built a vehicle unless required to do so, so it’s very important for the state to stay committed to this program requiring automakers to build small amounts in beginning years and then the market will take off." What do automakers blame for there being few electric cars now on the road（）
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