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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01 Mar 2013, 05:35
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Question Stats:

76% (02:10) correct 24% (01:00) wrong based on 93 sessions

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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 scientists 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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Last edited by fozzzy on 01 Mar 2013, 20:38, edited 2 times in total.
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Re: Healthy lungs produce a natural antibiotic that protects the [#permalink]

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01 Mar 2013, 06:25
IMO - C seems to be a better answer BUT the OA is D. Can someone please explain?

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

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01 Mar 2013, 07:11
Agree with rsaraiya; C it is.

The conclusion is : high salt concentration is what makes the antibiotic ineffective to people with cystic fibresis

According to the argument :
Healthy lungs produce a natural antibiotic that protects them from infection
People with cystic fibrosis 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
Now, let see the answer choices one by one :

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.
OUT OF SCOPE : We are concerned with people with cystic fibrosis not with people with healthy lungs.
B. A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
doesn't mention people with cystic fibresis, hence this option does'nt strenghten the argument
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 , this explains well why the antibiotic is ineffective while the salt concentration is HIGH because when normal , the antibiotic is known to be effective
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces.
the argument never mentioned synthetic antibiotic though it cannot be the correct answer
E. High salt concentrations have an antibiotic effect in many circumstances.
Clearly Irrelevant
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Re: Healthy lungs produce a natural antibiotic that protects the [#permalink]

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02 Mar 2013, 22:30
Straightforward question but the abnormally low rate of correct answers made me rethinking it over and over again.
Re: Healthy lungs produce a natural antibiotic that protects the   [#permalink] 02 Mar 2013, 22:30
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