The conclusion of the argument is: "Clearly, public health officials would be well advised to replace the previous Salmonella tests with the new test." Why? Conventional salmonella tests are slow and can miss unusual strains of Salmonella, which can be fatal if not identified quickly and treated. The new test, however, "identifies the presence or absence of Salmonella by the one piece of genetic material common to all strains."
We are looking for the answer choice that substantially weakens the argument.
Answer choice (B) is our answer because if the new test "detects the presence of Salmonella at levels that are too low to pose a health risk to people," then public health officials would not necessarily be well advised to replace the previous Salmonella tests with the new ones because the new ones might not help people. Detecting Salmonella levels too low to pose a health risk won't benefit the populace. Thus, answer choice (B) substantially weakens the argument.
Hope that was helpful! Let us know if you have any other questions.
AndyNovember 6, 2015
I'm not convinced that B truly does weaken the argument. Stating that the new test detects salmonella at rates too low to cause disease does not seem to imply that it cannot detect salmonella at rates which can cause disease.
Am I missing something?
MehranNovember 9, 2015
It may help to think of it this way. The new test will result in a lot of false positives. That is, people will test positive for Salmonella, because the new test will detect the microorganism, but presumably many of those people will have such low levels of the microorganism that they won't actually ever get sick. Using a test that generates a bunch of false positives is not good for public health, especially when the disease in question can in fact kill you if you don't quickly identify more serious cases.
Let us know if you have more questions, or if a further discussion of some of the other answer choice options might help!
