PrepTest 155

This is the contrapositive of the only diagrammable statement in the stimulus. So it must be true and is incorrect.

This is proven by the third sentence of the stimulus. We must repeat the liming process in lakes that are candidates for liming because the lake's water is consistently replaced. So this is another answer choice that must be true, making it incorrect.

Argument or Facts:
Facts

Question Type:
Must Be True (Bizarro)

Stimulus Summary:
Adding lime to lakes can help counteract the effects of acid rain. It neutralizes the acid, which prevents further damage and restores some of the health of already-damaged lakes. But you have to add more lime from time to time, because the water is being constantly replaced, taking the old lime with it. If the water in a lake is replaced more than once every six months, it's too expensive to treat that lake with lime.

Strategy Overview:

1. Argument or facts in passage?
   1. If argument, identify premises and conclusions
2. Sufficient/necessary conditions in the passage?
   1. If so, diagram statements and draw any deductions
3. For Bizarro questions, use anticipations to eliminate the answer choices that are absolutely 100% true

Answer Anticipation:
This is a Must Be True (Bizarro) question, which means all the incorrect answer choices must be true. We're looking to eliminate anything that the facts in the passage are sufficient to prove true. The correct answer is the one that's not necessarily true, based on the facts in the passage.

There's only one statement that we can diagram to diagram here:

1. Replaced more than once every six months -> Not a candidate for liming

So, incorrect answer choices could include the contrapositive of this diagrammable statement. They could also restate or combine the other pieces of information we learned about liming.

The correct answer choices might reverse the above conditional statement without negating it, or negate it without reversing it. Or, the correct answer choice might simply make a claim that's too strong to be supported by these premises or one that's outside the premises' scope.

Answer Choice Explanation:
We don't have enough information in the stimulus to determine whether this is true or false. None of the premises are about what acid rain does to unlimed lakes. It's all about the effects of liming and how often we should lime certain lakes. So, we can't say if this statement is true or false. That means this answer choice is not necessarily true, making it the correct answer.

Key Takeaway:
With these "Bizarro" question prompts, many students choose an incorrect answer simply because they didn't take the time to understand the criteria for a correct or incorrect answer. On a Bizarro Must Be True question, it's important to take a few seconds to rephrase "Must Be True EXCEPT" into "Not Necessarily True" or "Could Be False," before reminding yourself that "must be true" answer choices are incorrect.

This is proven by the second premise, which states that lime can restore the health of some lakes where damage due to acid rain has already occurred. So, it's another answer choice that must be true and thus is incorrect.

This answer choice just rephrases the final premise of the stimulus. While it does leave out the specifics (water replaced every six months or less), it is phrased so weakly that it still must be true according to the premises. To prove the weak claim that "it may not be economical to attack the effects of acid rain by liming," we only need to find one type of lake in which liming is too expensive. And the last sentence tells us there's definitely one such lake: one in which the water is replaced at least once every six months. So this is yet another answer choice that must be true.