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?
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.
此题为充要条件的逆否命题。
A是B的充要条件，那末他的逆否命题比正确！
非B推出非A
If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment, ---------〉If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.
参考答案E
思路：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
A. 原文没有说
B. 条件不对
C. 原文是一部分plants没有这种能力
D. 原文只说明并非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，没说some Leachate一定是被送去浇那些无此能力的植物。
我想请问在解释中
他说--A是B的充要条件
那末他的逆否命题比正确！-- 我不懂什么是充分条件
又
什么是必要条件
我原本以为
唯一可以逆命题的情况是
在
必要条件下
例如
当产生K才会造成F 且K是造成F的唯一条件
所以
当没有造成F就代表没有产生K 这样的反推是正确的
但是看到这题
他说A是B的充分条件
所以他的逆命题正确
我就不太懂了
谁可以帮我解释一下
什么时候逆命题才是正确??
而
充分条件
跟必要条件的差别?? 谢谢
是因为这个道理太简单了吗?? 怎么都没人回我??
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