- Tue Nov 07, 2017 5:32 pm
#41360
Hi Kelia,
The stimulus here hints at a causal explanation for bacterial contamination of water supplies and chlorination. However, it's a Must Be True question that doesn't give us enough information to make a causal link one way or another between chlorination of water supplies and bacterial contamination, so any answer choice that involves such a linkage would involve a leap of logic, logically invalid, and thus be incorrect. This makes this a difficult question to Prephrase, but will help us eliminate some Loser answer choices.
Answer choice (A) makes the direct causal link that we've already established as logically invalid given the info in the stimulus, so we can immediately eliminate it.
Answer choice (B) is based on a misreading of the first sentence of the stimulus, which explicitly states only that "water in deep aquifers does not contain disease-causing bacteria," not that it is completely bacteria free. So again, a quickly-eliminated Loser.
Answer choice (C) also relies on a misreading of the first sentence of the stimulus, asking test takers to falsely infer that because deep aquifers are the only water source listed and don't contain disease-causing bacteria, they must be the best source of municipal water supplies. Since we have no information as to how they compare to other potential sources of municipal water supplies, we can't infer that they are the best sources.
Asnwer choice (D) can be correctly inferred from the last sentence. If all 50 municipalities' water supplies met the regional standard for cleanliness, and the ones that were chlorinated had more bacterial contamination than the ones that weren't chlorinated, some bacterial contamination must be allowed under those standards.
Answer choice (E) relies upon misreading the last sentence. We haven't been given any information about either the effectiveness of chlorine(as there is no control for contamination in pipes/storage tanks) or the effectiveness of any other disinfectant (none other are even mentioned!). So (E) is unsupportable.
Hope this clears up any confusion!
