91. Leachate is a solution, frequently highly contaminated, that develops when water permeates a landifill’s site. If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment, generally in unpredictable quantities. A method must be found for disposing of leach ate. Most landfill leachate is sent directly to sewage treatment plants, but not all sewage plants are capable of handling the highly contaminated water.
Which one of the following can be inferred from the passage?
A.The ability to predict the volume of escaping landfill leachate would help solve the disposal problem.
B.If any water permeates a landfill, leachate will escape into the environment.
C.No sewage treatment plants are capable of handling leachate.
D.Some landfill leachate is sent to sewage treatment plants that are incapable of handling it.
E.If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.
我也不明白啊，前辈们！为什么E是对呀？原命题说的是landfill’s capacity to hold liquids 导致了Leachate escape，但是E相反嘛!所以，不明白，不明白~~作者: wangliming 时间: 2010-9-5 19:12
发完帖子后，整整再看了一个小时的关于充分、必要、充要条件的东西后，才总算明白了这道题。原来是之前的思维有错误了。
if and only if表示“当且仅当”，说明是一个充分必要条件，因此表示唯一性，也就是说引起B的原因只有A，A的发生就必然导致B的发生，A的不发生就必要导致B的不发生。B是A的必要条件，B的发生必然导致A的发生。
好像说得很绕口，肯定让人看得很混乱，所以，建议大家去看看关于这方面的解释，就好理解啦。
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