英语翻译（09四川E）All too often,a choice that seems sustainable (可持

英语翻译
（09四川E）
All too often,a choice that seems sustainable (可持续的) turns out on closer examination to be problematic.Probably the best example is the rush to produce ethanol (乙醇) for fuel from corn.Corn is a renewable resource — you can harvest it and grow more,almost limitlessly.So replacing gas with corn ethanol seems like a great idea.One might get a bit more energy out of the ethanol than that used t make it,which could still make ethanol more sustainable than gas generally,but that's not the end of the problem.Using corn to make ethanol means less corn is left to feed animals and people,which drives up the cost of food.That result leads to turning the fallow land一including,in some cases,rain forest in places such as Brazil 一into farmland,which in turn gives off lots of carbon dioxide (C02) into the air.Finally,over many years,the energy benefit from burning ethanol would make up for the forest loss.But by then,climate change would have progressed so far that it might not help.You cannot really declare any practice （“sustainable” until you have done a complete life-cycle analysis of its environmental (环境的) costs.Even then,technology and public policy keep developing,and that development can lead to unforeseen and undesired results.The admirable goal of living sustainably requires plenty of thought on an ongoing basis.
千万不要用翻译器。用了也不采取。要自己翻译。

经常有这种情况,一个看起来能够“持续发展”的选择,最终被证明存在很多问题.或许最好的例子就是,大家一拥而上地用玉米制造乙醇用作燃料.玉米是可再生资源—可以在收获后再种植更多,产量几乎没有限制.所以用玉米乙醇代替汽油看起来是个好主意.从乙醇中获得的能源或许比制造这些乙醇所耗费的能源要多一些,这使得总体上看来,乙醇是比汽油更具持续性的能源,但是问题还没有结束.
使用玉米制造乙醇意味着可供动物和人们食用的玉米减少,这将推动食品成本上涨.这个结果会导致一些休闲地（在一些情况下,包括位于巴西等地的热带雨林）被转化为农场,结果是很多二氧化碳被排放到空气中.最终,许多年之后,从燃烧乙醇中所获得的能源利得将用于弥补森林的损失.但是到那时,可能会出现气候变化如此急剧,以致于弥补损失也起不到作用的情况.
你无法真正宣布任何实践是能够“持续发展”的,除非你已对它的环境成本进行过彻底的周期分析.尽管如此,技术和公共政策仍在持续发展,而这种发展会导致无法预见的不良后果.“持续存在”的宏伟目标,需要在动态的基础上进行周密的思考后才能确定是否可行.