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

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17 Dec 2005, 10:37
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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 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 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.
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17 Dec 2005, 12:41
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17 Dec 2005, 20:40
I'll go with C.

If lungs can resist the bacteria when salt concentration is brought to normal and cannot resist it when the concentration is high, then it can be concluded that high level of salt concentration rather than any other factor makes antibiotic ineffective.

I think B is unsupported since the statement that antibiotic can function in unusually low salt concentration suggests that level of salt concentration is not a cause of ineffectiveness
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SVP
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19 Dec 2005, 03:45
I will leave it open for little more discussion.
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19 Dec 2005, 08:41
C.

C talks about the experiment done to see if the reverse of what is said in the document can be true.

B talks about the low concentration. I don't think we are concerned about it.
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23 Dec 2005, 11:10
OA is C.
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23 Dec 2005, 11:10
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