Healthy lungs produce a natural antibiotic that protects the

[JbhB682]

Source : GMAT prep

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 scientist's 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.

OA : c

[JbhB682]

Hi Experts - was wondering if my analysis on B was accurate.

B too me is just a re-statement of the premise (contrapositive)

Theory : If A refers to B, then one can infer that not B also refers to Not A

Premise : High salt concentration (A) CAUSES ineffectiveness (B)

Inference : Not B (effectiveness) is seen whenever Not A (not High concentration) is seen

Option B is just saying the antibiotic is effective (Not B) when situations of Not A (not High concentrations can be either of these concentrations Normal /Low/Very low concentrations) are seen

[esledge]

Yep, I'd say that's a correct assessment. (B) attempts to distract by going to the opposite extreme.

(B) introduces another variable (unusually low concentration of salt), rather than simply removing the variable in question (the high salt concentration) and using the normal/neutral salt concentration. (B) also fails to address lungs or cystic fibrosis patients, talking about just "an environment" instead.

In contrast, (C) does consider:
--the relevant lung tissue from the relevant people
--the removal of the factor (abnormally high salt concentration) that the scientists theorize is responsible, to see whether they are right.