[求助]gwd-5-26

ethyl

A：无关。没有将浓度与抗菌性结合；可能支持的是健康人可以自我恢复

B：错误比较。文中没有提到低浓度的情况；而且a sample没有代表性

C：事实型加强

D：Many lung infections can be treated，无关

E：太笼统，没有提供有效信息

bigbill

確實  C比B好的多多~~

carmenleaf

以下是引用girdle在2004-9-17 23:07:00的发言：

Q26:

Healthy lungs produce a natural antibiotic that protects them from infection by routinely killing harmful bacteria on airway surfaces.  eople with cystic fibrosis, however, are unable to fight off such bacteria, even though their lungs produce normal amounts of the antibiotic.  The fluid on a0.irway surfaces in the lungs of people with cystic fibrosis has an abnormally high salt concentration; accordingly, scientists hypothesize that the high salt concentration is what makes the antibiotic ineffective.

Which of the following, if true, most strongly supports the scientists’ hypothesis?

1. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.


2. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.


3. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.


4. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.  


5. High salt concentrations have an antibiotic effect in many circumstances.

answer : c

why b is incorrect?

有一个问题困扰我很久，借此题问一下各位：

结论：scientists hypothesize that the high salt concentration is what makes the antibiotic ineffective.

即：high salt concentration ——〉antibiotic ineffective.

那么与之等价的逆否命题则是：antibiotic effective.——〉normal salt concentration

而c选项：a normal salt concentration——〉tissue can resist bacteria则是原命题的否命题，与原命题不等价的呀，所以我坐看右看觉得都不对，不晓得是哪个地方分析错了。

   记得在上XDF的时候把费费给问郁闷了，没好意思再问，结果到现在还是不懂，麻烦大家指点一下呀

ayang1017

建议你看看陈向东那本逻辑，或者也许这个版面谁总结得也有吧。没错逆否是原命题得等价。但是在gmat里所考到得支持，并不需要是充分必要条件，他只需要这个条件得特点是增加了它结论更强，但增加它并不导致结论必然正确～我个人理解

tobytao

哎，我觉得C还是没啥道理，没道理说normal浓度时候antibiotic不起作用一定就能引出说high浓度antibiotic也不起作用啊。。

完全可以认为high浓度的时候antibiotic又发挥作用了啊。。这之间没有positive的关系的吧。。

郁闷啊。。哪位NN解释一下呢？

[此贴子已经被作者于2005-11-14 17:41:44编辑过]

乌龙茶

我觉得A比较靠谱。

通过antibiotic ineffective 反映出 high salt concentration

侧面事实支持作者hypothesis

cdsteven517

B 是武官选项嘛，CPA 很有用的。。。

eaststar

如果没有C,我认为B也可以选。

yhlin

这题选A

A选项说"salt concentration of the fluid on the airway surfaces of healthy people"提高后，会被回到正常的准位，代表”healthy people”需要正常盐浓度，支持了题目的结论。

反观C只说明在正常浓度，能抵抗细菌，无法支持结论”高浓度会造成antibiotic

失效"

ecochem

以下是引用carmenleaf在2005-9-5 17:04:00的发言：

有一个问题困扰我很久，借此题问一下各位：

结论：scientists hypothesize that the high salt concentration is what makes the antibiotic ineffective.

即：high salt concentration ——〉antibiotic ineffective.

那么与之等价的逆否命题则是：antibiotic effective.——〉normal salt concentration

而c选项：a normal salt concentration——〉tissue can resist bacteria则是原命题的否命题，与原命题不等价的呀，所以我坐看右看觉得都不对，不晓得是哪个地方分析错了。

   记得在上XDF的时候把费费给问郁闷了，没好意思再问，结果到现在还是不懂，麻烦大家指点一下呀

我觉得本题不是must be true题型，正确答案往往就是原论证结论的逆否命题

本题是support的题型，只要提供的信息能够支持结论就行，C选项support了结论。

如果选项中有逆否命题，我倒不觉得一定会是正确答案，因为逆否命题的信息，原文已经给出，此选项并没有提供更多的信息来support结论

一点拙见，欢迎讨论