[求助]LSAT-Test3-SectI-Q12

ruthere

12. Leachate is a solutions, frequently highly contaminated, that develops when water permeates a landfill site, If and only if the landfill's capacity to hold liquids is exceeded does the leachates escape into the environment, generally in unpredictable quantities, A method must be found for disposing of leachate. Most landfill leachate is send 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 send 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. 題目: If and only if the landfill's capacity to hold liquids is exceeded does the leachates escape into the environment 到底是 <1> leachates escape --> landfill's capacity is exceeded 還是 <2> landfill's capacity is exceeded --> leachates escape 那個是p, 那個是q?? 我把它想成是<1>了. 如果<1>是真, 那麼答案(e), 非p-->非q, leachate 非escape --> landfill's capacity非exceeded 為什麼對?? p-->q, 不是應該 非q-->非p 嗎? 請大俠指教這題如何解.

StephanieYun

你想得太繁了，

atongmu

A only if B是 A>B。因为B是A的必要条件，而某结果发生必然可推出导致其发生的必要条件的存在。
这道题是If and only if，所以A和B互为充要条件。

btw，楼主的思考过程是必要的，不是想得太繁。如果没有这个思考过程，就算选对了答案，也不会知道为什么对！

ruthere

以下是引用atongmu在2003-4-17 9:57:44的发言： A only if B是 A>B。因为B是A的必要条件，而某结果发生必然可推出导致其发生的必要条件的存在。 这道题是If and only if，所以A和B互为充要条件。 btw，楼主的思考过程是必要的，不是想得太繁。如果没有这个思考过程，就算选对了答案，也不会知道为什么对！

謝謝. "if and only if" 是A<-->B 的關係. 所以答案e也就對了.