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OFFICIAL EXPLANATION



Several gastrointestinal illnesses are contracted by swimming in the sea as a result of infectious bacteria in the water. There are tests which reveal the existence of these bacteria, but they are not reliable. Therefore, the authorities have decided not to invest money in those tests, but rather in tests which reveal the existence of non-infectious bacteria.

Which of the following supports the authorities' decision?



A. Non-infectious bacteria were always found close to shore.

Incorrect.

To solve this Conclusion Strengthening question, first break down the argument. The first two sentences are premises which provide factual data; the last sentence includes a conclusion conjunction (therefore) so it's the conclusion:

    Premise A: infectious bacteria in the sea cause illness +Premise B: tests designed to locate such bacteria are unreliable =Conclusion: use tests that locate non-infectious bacteriaPossible assumption: finding non-infectious bacteria is somehow beneficialStrengthening Data: ?


You are required to find data that supports investing in non-infectious bacteria tests or detracts from investing in infectious bacteria tests. The correct answer could be one that confirms the argument's assumption.

This answer choice neither strengthens nor weakens the authorities' decision, as the location in which non-infectious bacteria were found does not help us decide which test to use.



B. Where the non-infectious bacteria are found, the infectious bacteria are also found.

This answer choice confirms the argument's assumption: if the non-infectious bacteria exist close to infectious bacteria, the more reliable non-infectious bacteria tests could provide a good indication to whether infectious bacteria are present.


C. The test which reveals the existence of non-infectious bacteria was developed only recently.

Incorrect.

To solve this Conclusion Strengthening question, first break down the argument. The first two sentences are premises which provide factual data; the last sentence includes a conclusion conjunction (therefore) so it's the conclusion:

    Premise A: infectious bacteria in the sea cause illness +Premise B: tests designed to locate such bacteria are unreliable =Conclusion: use tests that locate non-infectious bacteriaPossible assumption: finding non-infectious bacteria is somehow beneficialStrengthening Data: ?


You are required to find data that supports investing in non-infectious bacteria tests or detracts from investing in infectious bacteria tests. The correct answer could be one that confirms the argument's assumption.

At best, this answer choice indirectly weakens the authorities' decision: if the test is new, its efficiency is yet to be proven. This makes the authorities' decision to invest in this test even less understandable and justified.



D. Tests which reveal the existence of non-infectious bacteria take less time and cost less money.

Incorrect.

While this answer choice could possibly be seen as strengthening the authorities' decision, it still provides no clear justification for the decision (if the test is pointless, its efficiency is not a great help). There is an answer choice which strengthens the conclusion more clearly. Remember that the correct answer to a Critical Reasoning question should be as simple and straightforward as possible.



E. One in every ten people who swims in the sea contracts a gastrointestinal illness as a result of infectious bacteria in the water.

Incorrect.

This answer choice neither strengthens nor weakens the authorities' decision; it simply adds more information to that given in premise A, without supporting the use of non-infectious bacteria tests.
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