Critical Reasoning

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 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.

IMO-B. If C is the right answer, pls explain?

This is y I selected C.... I find B also complelling but the subject of the arg is lungs nd B focuses on antibodies. C rightly focuses on lung tissue. I arrived at C by POE

Surely C

Healthy lungs produce a natural antibiotic that protects them from infection by routinely k!II!ng 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 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 -->irrelvant
B. A sample of the antibiotic was capable of k!II!ng bacteria in an environment with an unusually low concentration of salt -->this is a weaken. "unusually low concentration of salt" means an average antibiotic usually demolish k!II!ng bacteria in high ambience concentrating of salt --> this weaken 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 --> best. the argument is "high salt concentration is what makes the antibiotic ineffective" which also means "lower salt concentration can make the antibiotic more effective". Here, "normal" means lower than "high" --> strengthen
D. Many lung infections can be treated by applying synthetic antibiotics to the airway surfaces --> irrelevant
E. High salt concentrations have an antibiotic effect in many circumstances -->weaken

IMO-B. If C is the right answer, pls explain?[/quote]

thanks guys!!

After eliminating A, D and E, we are left to choose between B and C.

B) The key word to note here is "unusually low" and it means lower than normal which take is actually misleading and goes against the passage.

C)-Clearly states that with a "Normal" salt content, the bacteria is resisted and hence we can conclude that the amount of salt determines the effectiveness of the antobodies.

Hope this helps

I will go with option C

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 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.

C says that tissue can resist bacteria in normal salt solution. It says nothing about high salt concentration of the solution. It says nothing about the antibiotic becoming ineffective. In fact the antibiotic can still remain effective in the salt solution and act alongside salt solution in resisting the effect of bacteria.

Experts, please comment.

crackgmat007 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 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 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.

The argument concludes that a high salt concentration in people with cystic fibrosis CAUSES their inability to resist bacteria.
One way to strengthen a causal argument is to show the following:
If the cause is removed, the effect does not happen.
C: When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
Here, the cause is removed (the high salt concentration is replaced with a normal salt concentration), and the effect does not happen (the tissue from people with cystic fibrosis is able to resist bacteria), STRENGTHENING the conclusion that a high salt concentration in people with cystic fibrosis CAUSES their inability to resist bacteria.

The correct answer is C.

GMATGuruNY wrote:

crackgmat007 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 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 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.

The argument concludes that a high salt concentration in people with cystic fibrosis CAUSES their inability to resist bacteria.
One way to strengthen a causal argument is to show the following:
If the cause is removed, the effect does not happen.
C: When lung tissue from people with cystic fibrosis is maintained in a solution with a normal salt concentration, the tissue can resist bacteria.
Here, the cause is removed (the high salt concentration is replaced with a normal salt concentration), and the effect does not happen (the tissue from people with cystic fibrosis is able to resist bacteria), STRENGTHENING the conclusion that a high salt concentration in people with cystic fibrosis CAUSES their inability to resist bacteria.

The correct answer is C.

Dear GMATGuru

Why B is wrong? When there is low concentration of slat, the antibiotic kills the bacteria.

Thanks

Mo2men wrote: Dear GMATGuru

Why B is wrong? When there is low concentration of slat, the antibiotic kills the bacteria.

Thanks

In the CR above, the cause = a NORMAL salt concentration (seen in healthy lungs) is replaced with a HIGH salt concentration (seen in people with cystic fibrosis).

B: A sample of the antibiotic was capable of killing bacteria in an environment with an unusually low concentration of salt.
This option does not simply remove the cause (leaving a normal salt concentration) but discusses an entirely NEW situation (an UNUSUALLY LOW salt concentration).
Since neither healthy people nor people with cystic fibrosis have an unusually low salt concentration, the information in B is irrelevant.
Eliminate B.