A
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 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 lifecycle analysis of its environmental 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.
语篇解读： 本文是一篇议论文。文章主要谈论了可持续性发展的判断依据以及相关的一些事实。
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.
解析：选C 细节理解题。根据第二段中的“That result leads to turning the fallow land — including, in some cases, rain forest in places such as Brazil”可知，对于农田的需要导致森林被砍伐，故选C项。
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
解析：选A 代词指代题。根据画线词上文中的“Finally, over many years, the energy benefit from burning ethanol would make up for the forest loss.”可知，it指前文提到的the energy benefit。故选A项。
3．What does the author mainly discuss in the text?
A．Technology.
B．Sustainability.
C．Ethanol energy.
D．Environmental protection.
解析：选B 主旨大意题。通过全文可知，作者主要谈论的是可持续性的判断依据以及相关的一些事实，故选B。
