Healthy lungs produce a natural antibiotic that protects : GMAT Critical Reasoning (CR)
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# Healthy lungs produce a natural antibiotic that protects

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Healthy lungs produce a natural antibiotic that protects [#permalink]

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20 Sep 2004, 06:25
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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. The fluid on airway 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 scientistsâ€™ hypothesis?

A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
E. High salt concentrations have an antibiotic effect in many circumstances.
[Reveal] Spoiler: OA
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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13 Mar 2005, 22:21
B (in low concentrations, antibiotic is effective - so it is the high salt concentration that makes the antibiotic ineffective)
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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13 Mar 2005, 22:44
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1) healthy lungs produce natural antibiotic

2) antibiotic protects lungs from infection by routinely killing harmful bacteria on airway surface

3) people with cystic fibrosis are unable to fight off bacteria, even when lungs produce normal amounts of antibiotics

4) Fluid on airway surfaces in lungs of people with cystic fibrosis has an abnormally high salt concentration

5) scientist hypothesize that high salt concentration is what makes the antibiotic ineffective <-- conclusion

We want an answer that supports the conclusion

A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.
- Does not say salt concentration renders antibiotic ineffective

B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
- Only supports low concentration salt premise

C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
- This chioce supports the conclusion that high salt concentration in people with cystic fibrosis renders the antibiotic useless.

D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
- Tells us nothing

E. High salt concentrations have an antibiotic effect in many circumstances.
- Negative effect or positive effect. Not stated here. E is out.

C it is.
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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13 Mar 2005, 22:46
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Between B and C, i went with C. B states that the antibiotic was effective in killing bacteria only in unusally low concentrations of salt. But do we know if a normal person has unusally low salt concentration ?? We do not, but we do know that their salt concentration would more or less be at a normal level. (whether this normal level is high or low does not matter, it's normal on the average). The word 'unusally' is too limiting.
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 00:48
clearly C for me

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

In my opinion :
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
no information at all, we just know the antibiotic can kill bacteria when there is a low concentration of salt however the issue raised here is only when there is a high salt concentration. So it's totally useless to know the action of the antibiotic in a low salt environnement. Moreover, choice B doesn't clearly precise whether the sample of the antobiotic is coming from people with cystic fibrosis or not...
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 00:51
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marine wrote:
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. The fluid on airway 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 scientistsâ€™ hypothesis?

A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal.
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
E. High salt concentrations have an antibiotic effect in many circumstances.

C it is.

People with cystic fibrosis has an abnormally high salt concentration, and high salt concentration causes they cannot to fight off such bacteria.

No high salt concentration makes people with cystic fibrosis be able to fight off such bacteria.

An typical question.

If A, then B. If not A, then not B.
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 06:19
I am torn between B and C. They seem to be both equally likely
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 06:36
It is C because all the three necessary are covered.. salt solution, cystic fibrosis and effects of the same tissue from people who had cystic fibrosis in normal levels of salt solution..
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 07:43
Problem with B is it talks about low salt concentration, while what we need to know is normal versas high salt concentration.
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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14 Mar 2005, 08:38
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Folaa3 wrote:
I am torn between B and C. They seem to be both equally likely

Note also the use of 'unusally low salt cocentration' in (B). How low is low, we do not know.
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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13 Jul 2014, 00:45
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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31 May 2015, 20:40
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. The fluid on airway 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?

Conclusion : high salt concentration is what makes the antibiotic ineffective

A. When the salt concentration of the fluid on the airway surfaces of healthy people is raised artificially, the salt concentration soon returns to normal
This option talks about that if the salt concentration of the fluid is brought up, the salt concentration returns to normal. This option doesn't provide any information why or how high salt concentration makes the antibiotic ineffective

B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
This is as per premise that antibiotic is effective in low concentration of salt

C. When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
Correct as it supports that if the salt concentration is brought back to normal, the natural antibiotic is effective.

D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
Out of scope as we are not concerned with "Synthetic Antibiotics"

E. High salt concentrations have an antibiotic effect in many circumstances.
Out of scope as in many circumstances high salt concentrations have an antibiotic effect but we are concerned with this particular scenario
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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31 May 2015, 20:54
C
Conclusion - the high salt concentration is what makes the antibiotic ineffective.
Strengthen - lung tissue can resist bacteria in normal salt concentration
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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11 Jun 2016, 08:52
What is the source of this question? Option C means tissue from dead people or what?
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Re: Healthy lungs produce a natural antibiotic that protects [#permalink]

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01 Dec 2016, 04:25
Dear Experts and mikemcgarry
although I picked up C, I still want to make clear that the difference between causality and relevance

the conclusion in this case is that high salt concentration is what makes the antibiotic ineffective.

I think that high salt concentration is the cause of antibiotic ineffective, because it makes antibiotic ineffective. IMO, the word "makes" indicates that high salt concentration directly results in the antibiotic ineffective.

in other word, scientists establish the cause - effect relationship between high salt concentration and ineffective antibiotic.

Am I right?

if not, please point out my fault.

thanks a lot

have a nice day.
>_~
Re: Healthy lungs produce a natural antibiotic that protects   [#permalink] 01 Dec 2016, 04:25
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