GWD-24-15.ＮＮ，ＨＥＬＰ

云的足迹

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.

答案是Ｄ，自己理解也懂些，似乎在说原因与沿浓度无关，但是我做的时候选Ａ了，盐浓度会恢复到正常，当时是觉得应该就与高浓度的盐的关系不大了，我这么想错在哪里呢？请ＮＮ帮忙分析一下，谢谢哦

Winterfish

我觉得这题既然是WEAKEN题型，当然还是直接反驳结论的好了。

科学家观察到病人和健康人唯一不同的特征是盐的浓度高，就得出结论是盐的浓度妨碍了病人抗体抵御能力。如何削弱？直接反击论据不成立，或者找他因来排除。这里显然D反击有力：病人即使盐的浓度正常，也不能抵御细菌入侵。就是说盐无关。

A选项是说健康人的生理，关于病人只字未提。（没有比较就没有结论，只谈了一个事实）推理过程：健康人体内的盐浓度能自动调节，只能暗示病人的盐浓度不能自动调节。到底和抗体抵御细菌能力有无关系？还是没有结论吧。

这个题的难度在专业术语多，容易被它搞晕。我最近也在看逻辑，做题一塌糊涂，都是看了答案才明白的。当然，不明白的更多，一起努力吧。

mingyuexing

 A选项没有将高浓度的盐和抗体的有效性联系起来

sumerlaw

其实A是支持的

因为文章的逻辑就是将不能成功的fight off bacteria 归结于高浓度的 salt 

D直接削弱说低浓度时也无用

A说健康的肺盐浓度高一会之后又会降到正常水平（时间很短），侧面支持了，健康的lung能在正常盐浓度下杀死细菌