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 to 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 –including, in some cases, rain forest in places such as Brazil—into farmland, which in turn gives off lots of carbon dioxide (CO) 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 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.
小题1:What might directly cause the loss of the forest according to the text?
A．The growing demand for energy to make ethanol
B．The increasing carbon dioxide in the air
C．The greater need for farmland
D．The big change in weather.小题2:The underlined word “it” in the second paragraph refers to “ ”
A．the energy benefit
B．the forest loss
C．climate change
D．burning ethanol小题3:The author thinks that replacing gas with corn ethanol is .
A．impractical
B．acceptable
C．admirable
D．useless小题4:What does the author mainly discuss in the text?
A．Technology
B．Sustainability
C．Ethanol energy
D．Environmental protection
小题1:C
小题2:A
小题3:A
小题4:B
题目分析：作者主要谈论的是可持续性发展的判断依据以及用相关一些事实来进行佐证其论点。
小题1:C推理判断题。注意问的是直接原因。That result leads to turning the fallow land — including, in some
cases, rain forest in places such as Brazil — into farmland(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)。
小题2:A词义猜测题。根据上下文可知是指能源优势。
小题3:A推理判断题。根据全文可知作者认为用corn代替gas是不符合实际的，会带来很多意想不到的问题。
小题4:B主旨大意题。读完全文我们可以知道，作者主要谈论的是可持续性发展的判断依据以及用相关一些事实来进行佐证其论点。该题容易误选D。