GWD-24-15.

Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces. People with cystic fibroses, 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 bas 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?

1. 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.

2. The antibiotic produced by the lungs is effective at killing harmful bacteria even when salt concentrations are below levels typical of healthy lungs.

3. 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.

4. 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.

5. 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.

题干一样，上次问support ，这次问weaken。但是选项难好多。

正确答案是D，就是上次support正确答案取非，可是我觉得效果完全不同。如果说因为盐的浓度上升破坏了lung中produce a natural antibiotic 的功能，那么之后再降低也无法生产，也很正常啊。没有weaken。

还有，A错在哪里？是不是a relatively short period of time.不好？

C呢？不明白“after having been reduced to levels typical of healthy lungs.”的意思，是不是多了这个所以错了?

题干中问 以下选项作为 an experimental result    有没有weaken

若A项是个实验结果  则说明  healthy lungs 它有从 high salt

concentration  到正常的这样一个能力

同理      C项是说明   people who suffer from cystic fibrosis    把他的 salt  concentration  降到正常水平 结果还是回来

A C 两项都没有 正面说明    是不是由于  high salt concentration   导致 antibiotic  起不到应有的效果

而D项 正中要害    对于people who suffer from cystic fibrosis   即使把

high salt concentration  降到正常水平  antibiotic  仍旧不能起到抵御作用

正是对问题中 假设 high salt concentration 使antibiotic  起不到作用   最强力的WEAKEN

原文说的是People with cystic fibroses-------abnormally high salt

concentration------antibiotic becomes ineffective。所以科学家假设

abnormally high salt concentration导致antibiotic becomes ineffective

A说的是normal salt concentration 的情况，所以无关

C重复了原文的信息。所以不能减少原文证据对结论的说服力。最多对原文证据是个正面的作用，就是SUPPORT结论

D说的是即时没有原因（没有abnormally high salt concentration），结果一样有。无因---有果型削

想再问问，不好意思

D中有“reduced”说明先升上去了，后来有降下来。那么是否可能存在我说的那种情况呢？

“如果说因为盐的浓度上升破坏了lung中produce a natural antibiotic 的功能，那么之后再降低也无法生产”

还有A说的是在“salt concentration has substantially increased”的lungs，说的意思是不是“在增加盐浓度的肺有自己修复功能，在一小段时间内把浓度降回到正常水平”？

还是不懂C在说什么：（