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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?


Option 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.

Option B:

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

Option C:

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

Option D:

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

Option E:

High salt concentrations have an antibiotic effect in many circumstances.

Difficulty Level



Option C is the right answer.

Option Analysis

Question type: Strengthen the Argument

Summary of the argument: The argument assumes that high salt content makes the antibiotic ineffective–There is a clear causality. Now we must be finding an answer choice that supports this statement.

A) This option only talks about salt concentration. This doesn’t talk about the effect on the antibiotic.

B) We are worried about high concentrations of salt and its effect on antibiotics. This option doesn’t talk about the same.

C) Correct Answer

D) The option doesn’t talk about synthetic antibiotics.

E) This is a very generalized answer. Doesn’t serve our purpose.

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