阅读理解。
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 makeit, 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.
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.
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
3. The author thinks that replacing gas with corn ethanol is _____.
A. impractical
B. acceptable
C. admirable
D. useless
4. What does the author mainly discuss in the text?
A. Technology
B. Sustainability
C. Ethanol energy
D. Environmental protection

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