请教狒狒91和94

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 queantities. A method must be found for disposing of leachate. 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.

不是很理解题目的意思，

A reasoning error in the argument is that the argument

(A) attempts to infer a value judgement from purely factual premises

(B) attributes to every member of the population the properties of the average member of the population

(C) fails to take into account what proportion of the population have used cocaine

(D) ignores the fact that some cocaine users do not test positive

(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine

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 queantities. A method must be found for disposing of leachate. Most landfill leachate is sent directly to sewage treatment plants, but not all sewage plants are capable of handling the highly contaminated water.

题目是说：leachate 是一种溶液，这种溶液是高度受到污染的并且是渗透在landfill里的。只有当leachate在landfill达到饱和后才会对环境造成污染（因为流入了环境）。所以必须想出一种方法来处理这些leachate,大部分的leachate都被送往sewage plant处理，但并不是所有的sewage plant都能够处理得过来。

简单得跟你解释下，不是很好，请多多包涵

94题:我觉得详解版的解释很精辟,LZ可以体会一下

我理解的意思就是：如果加入人群里面本来加入吸毒的比例很低，那个Random group就有可能是，其中有99%的人都不吸毒，只有1%的人吸毒，所以如果100个人的group，那么就有忧positive结果的人里面，可能就会有5个不吸毒的，1个要吸毒的，所以吸毒的不可能里面是majority。

题是明白了 可是为什么D不对呢？ 我认为D比E好啊因为only if 是只有才 而不是只要就，是必要非充分条件啊，所以不存在A推B，那不就没有B否推A否了？

而题中说了not all sewage plants are capable of handling the highly contaminated water.不就说明Some landfill leachate is sent to sewage treatment plants that are incapable of handling it吗？