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题库 / Prep2008E1-CR-105
Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces. People with cystic fibrosis, however, are unable to fight off such bacteria, even though their lungs produce normal amounts of the antibiotic. Since the fluid on airway surfaces in the lungs of people with cystic fibrosis has an abnormally high salt concentration, scientists hypothesize that in high-salt environments the antibiotic becomes ineffective at killing harmful bacteria.
Which of the following, if it were obtained as an experimental result, would most decisively undermine the scientists' hypothesis?
Healthy lungs in which the salt concentration of the airway-surface fluid has been substantially increased are able to reestablish their normal salt concentration within a relatively short period of time.
The antibiotic produced by the lungs is effective at killing harmful bacteria even when salt concentrations are below levels typical of healthy lungs.
The salt concentration of the airway-surface fluid in the lungs of people who suffer from cystic fibrosis tends to return to its former high levels after having been reduced to levels typical of healthy lungs.
The lungs of people who suffer from cystic fibrosis are unable to fight off harmful bacteria even when the salt concentration is reduced to levels typical of healthy lungs.
The salt concentration in the airway-surface fluid of people whose lungs produce lower-than-average amounts of the antibiotic is generally much lower than that typical of healthy lungs.
情景：健康的肺能生产自然的抗体。但是，有囊肿性纤维化病的病人却不能攻击入侵的细菌。研究发现，这些病人肺中的含盐量很高。因此，科学家认为是高盐度让抗体失效的。
推理：
前提：anabnormally high salt concentration和the antibioticineffective之间存在正相关关系
结论：The high salt concentration is what makes theantibiotic ineffective
答案预估：
其它能解释为何“抗生素无效”的原因不存在。
“高盐度导致抗生素无效”的其它必要条件（常理上能保真推理出的一切结果）。
选项分析：本题选项的形式和104题虽然有区别，但是内核几乎一致。问法也差不多。在此不过多赘述。按照相关因果的推理方式找到答案即可。
答案选项为(D)。
A选项：略
B选项：略
C选项：略
D选项：略
E选项：略
D. 即使盐浓度正常也还是无法杀死病菌说明与盐浓度高没有关系
相关因果推理，要么找与因果都相关的，要么找解释果的他因。D选项说即使在盐浓度恢复到正常水平时得病的人的肺还是不能抵抗病毒。这是削弱了因果联系。
C E只说明了盐浓度，并没有说明抗体无效的原因。不要脑补！