逻辑中的一个问题

戴小真 · 发表于 2012-6-9 09:26:14

哪位高手可以解答下如何判定逻辑题中的条件是不是充要条件啊？
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.

本题的解释是E，逻辑思维就是“原文说：“Leachate（浸析液）是一种水渗透过垃圾填埋地后生成的溶液，这种溶液通常是高度污染的。当且仅当超出垃圾填埋的容水能力时（A），Leachate会泄露到外界环境中（B）。必须找到一种处理L的方法。许多L被送去用于污水灌溉，但不是所有的污水灌溉的植物都有能力处理这种被高度污染的水”。
原文中If and only if A then B(从B可推出A)；选项E为If not A then not B（非A推非B）正确

我很困惑就是我们在做GAMT逻辑的时候，A推B，很多不能选非A推非B，只能选非B推非A，

所以想知道如何区别A是B的充分条件还是充要条件。

戴小真 · 发表于 2012-6-9 09:37:35

还有一题

Zelda: Dr. Ladlow, a research psychologist, has convincingly demonstrated that his theory about the determinants of rat behavior generates consistently accurate predictions about how rats will perform in a maze. On the basis of this evidence, Dr. Ladlow has claimed that his theory is irrefutably correct.
Anson: Then Dr. Ladlow is not a responsible psychologist, Dr. Ladlow’s evidence does not conclusively prove that his theory is correct. Responsible psychologists always accept the possibility that new evidence will show that their theories are incorrect.

100. Which one of the following can be properly inferred from Anson’s argument?
(A) Dr. Ladlow’s evidence that his theory generates consistently accurate predictions about how rats will perform in a maze is inaccurate.
(B) Psychologists who can derive consistently accurate predictions about how rats will perform in a maze from their theories cannot responsibly conclude that those theories cannot be disproved.
(C) No matter how responsible psychologists are, they can never develop correct theoretical explanations.
(D) Responsible psychologists do not make predictions about how rats will perform in a maze.
(E) Psychologists who accept the possibility that new evidence will show that their theories are incorrect are responsible psychologists.

我本来选E，但是解释是”e. Another typical wrong answer. A ? B does not equal to B ? A. Basic logic error.“

逻辑中的一个问题

所属分类: GMAT考试

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