C vs. B

^ Basically I thought, regardless of the level detected, the stimulus is about replacing the test with one that is better than old one. If anything, I thought this added to its effectiveness. Then with C, I thought it hinted at the vagueness of the definition that was given. If there are several dangerous microorganisms that fit the definition, I thought this could mean the test is likely to give false positives.

Hi @SarahT, Happy to help! We are looking for an answer choice which weakens the conclusion that "public health officials would be well-advised to replace the previous Salmonella tests with the new test." This does not mean that the correct answer choice has to render the conclusion incorrect; it simply has to bring up new information that would weaken the conclusion. Answer choice (B) does this by presenting a flaw with the new tests. If the new tests detect Salmonella at levels that are too low to pose a health risk to people, then the new test will give many false positives. This could induce people to seek out health care when it is not necessary to do so, cause people to avoid foods they do not need to, or both! Answer choice (C) is incorrect because neither the new test nor the old test is designed to identify a variety of food-borne microorganisms that can cause intestinal illness. The tests are only designed to detect Salmonella; therefore, it is unlikely that either test would give false positives. Answer choice (C) would hint at vagueness in the definition of Salmonella if it discussed various strains of Salmonella. However, as it discusses various food-borne microorganisms, it is out of scope. Hope this helps! Please let us know if you have any further questions.

Ok. But the stimulus only pertains to detecting salmonella. What does it matter if it is low or high risk to health? According to the language of the stimulus, it still detected salmonella. What am I missing?

@dmorg517 Agreed! Can a thorough explanation be provided, I struggled due to that exact same reason.