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#60356
Complete Question Explanation
Must Be True—SN. The correct answer choice is (C)
For most test takers, this is the hardest question in the section so far. The stimulus contains multiple conditional statements, each of which is also qualified or limited in some way. Much of the difficulty here lies in appropriately diagramming these statements and drawing proper inferences from each one. To best attack this question, consider each sentence individually and attempt to make inferences by combining the sentences based on their common terms (the conditional indicators are italicized).
1. “Failure to rotate crops depletes the soil’s nutrients gradually unless other preventive measures are taken.”
To diagram this sentence, ask yourself, “How can I know for sure that this soil’s nutrients have been gradually depleted?” The only way to ensure that nutrient depletion has occurred is to verify that the crops have not been rotated and no other preventive measures were taken. Diagrammatically:
RC
D 
or
PM
That is, if the soil’s nutrients are not depleted, than either the crops were rotated or other preventive measures were taken.
2. “If the soil’s nutrients are completely depleted, additional crops cannot be grown unless fertilizer is
applied to the soil.”
This sentence can be diagrammed similarly to the first sentence:
D
AC or
F
That is, if additional crops are grown, the soil is either not completely depleted or fertilizer was applied. This inference can be linked to the contrapositive of sentence one through identifying the common term D, creating an additive inference and removing the common term. This yields the inference that if additional crops are grown then the crops were rotated, other preventive measures were taken, or fertilizer was applied.
The final two sentences should be evaluated, but need not be diagrammed. Taken together, these sentences indicate that, “all other things being equal,” vegetables grown in fertilized soil are more vulnerable to insects, need more pesticide, and pose a greater risk to human health than vegetables grown in non-fertilized soil.
Finally, the question stem indicates that vegetables were grown without fertilizer. Using the contrapositive of sentence two, one can immediately conclude that the soil in which these vegetables grew was not completely depleted of nutrients (crops require either fertilizer or non-depleted soil; these vegetables did not have fertilizer, so the soil could not have been completely depleted of nutrients). And from the contrapositive of the first sentence, if the soil’s nutrients are not completely depleted, then either the crops were rotated or other preventative measures were taken (at least one of these two conditions must occur). So what must be true is that the soil’s nutrients are not completely depleted, and that either the crops were rotated or other preventative measures were taken.
Answer choice (A): One can know that the soil’s nutrients are not completely depleted, because if the soil was completely depleted of nutrients, and the vegetables were not given fertilizer, the vegetables could not grow (from the contrapositive of sentence two). Since the vegetables grew without fertilizer, the soil could not have been completely depleted of nutrients.
Answer choice (B): Answer choice (B) is not correct because it is very much possible that these vegetables grew in soil in which crops had been rotated. Remember, either the crops were rotated or other preventative measures were taken.
Answer choice (C): This is the correct answer choice. This answer choice begins well – “The vegetables were grown in soil that had not been completely depleted of nutrients” – but then becomes somewhat more confusing when it states, “but not necessarily soil in which crops had been rotated.” Is crop rotation the only explanation for why the soil had not been completed depleted of nutrients? No. From the contrapositive of the first sentence, when soil’s nutrients are not completely depleted, then either the crops were rotated or other preventative measures were taken. So the crops do not have to be rotated (it is not necessary) as long as other preventative measures were taken.
Answer choice (D): This answer choice is incorrect because it cannot be clearly known whether pesticides are the actual cause of health risks to humans who eat the vegetables (although answer choice (D) does seem to contradict the last sentence: the stimulus states that the more pesticides used on vegetables, the greater the health risks to humans, which goes against this answer choice).
Answer choice (E): Much like answer choice (D), answer choice (E) contradicts the last sentence of the stimulus, which states that the more pesticides used on vegetables, the greater the health risks to humans. Thus vegetables treated with pesticides would pose a greater risk than vegetables that were not treated with pesticides.
Must Be True—SN. The correct answer choice is (C)
For most test takers, this is the hardest question in the section so far. The stimulus contains multiple conditional statements, each of which is also qualified or limited in some way. Much of the difficulty here lies in appropriately diagramming these statements and drawing proper inferences from each one. To best attack this question, consider each sentence individually and attempt to make inferences by combining the sentences based on their common terms (the conditional indicators are italicized).
1. “Failure to rotate crops depletes the soil’s nutrients gradually unless other preventive measures are taken.”
To diagram this sentence, ask yourself, “How can I know for sure that this soil’s nutrients have been gradually depleted?” The only way to ensure that nutrient depletion has occurred is to verify that the crops have not been rotated and no other preventive measures were taken. Diagrammatically:
- RC = rotate crops
D = soil’s nutrients depleted
PM = other preventive measures taken
RC
+ D
PM
RCD
or PMThat is, if the soil’s nutrients are not depleted, than either the crops were rotated or other preventive measures were taken.
2. “If the soil’s nutrients are completely depleted, additional crops cannot be grown unless fertilizer is
applied to the soil.”
This sentence can be diagrammed similarly to the first sentence:
- D = soil’s nutrients depleted
AC = additional crops grown
F = fertilizer applied
D
+ AC
F
DAC
or FThat is, if additional crops are grown, the soil is either not completely depleted or fertilizer was applied. This inference can be linked to the contrapositive of sentence one through identifying the common term D, creating an additive inference and removing the common term. This yields the inference that if additional crops are grown then the crops were rotated, other preventive measures were taken, or fertilizer was applied.
The final two sentences should be evaluated, but need not be diagrammed. Taken together, these sentences indicate that, “all other things being equal,” vegetables grown in fertilized soil are more vulnerable to insects, need more pesticide, and pose a greater risk to human health than vegetables grown in non-fertilized soil.
Finally, the question stem indicates that vegetables were grown without fertilizer. Using the contrapositive of sentence two, one can immediately conclude that the soil in which these vegetables grew was not completely depleted of nutrients (crops require either fertilizer or non-depleted soil; these vegetables did not have fertilizer, so the soil could not have been completely depleted of nutrients). And from the contrapositive of the first sentence, if the soil’s nutrients are not completely depleted, then either the crops were rotated or other preventative measures were taken (at least one of these two conditions must occur). So what must be true is that the soil’s nutrients are not completely depleted, and that either the crops were rotated or other preventative measures were taken.
Answer choice (A): One can know that the soil’s nutrients are not completely depleted, because if the soil was completely depleted of nutrients, and the vegetables were not given fertilizer, the vegetables could not grow (from the contrapositive of sentence two). Since the vegetables grew without fertilizer, the soil could not have been completely depleted of nutrients.
Answer choice (B): Answer choice (B) is not correct because it is very much possible that these vegetables grew in soil in which crops had been rotated. Remember, either the crops were rotated or other preventative measures were taken.
Answer choice (C): This is the correct answer choice. This answer choice begins well – “The vegetables were grown in soil that had not been completely depleted of nutrients” – but then becomes somewhat more confusing when it states, “but not necessarily soil in which crops had been rotated.” Is crop rotation the only explanation for why the soil had not been completed depleted of nutrients? No. From the contrapositive of the first sentence, when soil’s nutrients are not completely depleted, then either the crops were rotated or other preventative measures were taken. So the crops do not have to be rotated (it is not necessary) as long as other preventative measures were taken.
Answer choice (D): This answer choice is incorrect because it cannot be clearly known whether pesticides are the actual cause of health risks to humans who eat the vegetables (although answer choice (D) does seem to contradict the last sentence: the stimulus states that the more pesticides used on vegetables, the greater the health risks to humans, which goes against this answer choice).
Answer choice (E): Much like answer choice (D), answer choice (E) contradicts the last sentence of the stimulus, which states that the more pesticides used on vegetables, the greater the health risks to humans. Thus vegetables treated with pesticides would pose a greater risk than vegetables that were not treated with pesticides.