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#7 - Failure to rotate crops depletes the soil's nutrients

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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 = rotate crops
    D = soil’s nutrients depleted
    PM = other preventive measures taken

    RC
    + ..... :arrow: ..... D
    PM

The contrapositive thus becomes:

..... ..... ..... RC
D ..... :arrow: ..... 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 = soil’s nutrients depleted
    AC = additional crops grown
    F = fertilizer applied

    D
    + ..... :arrow: ..... AC
    F

The contrapositive is:

..... ..... ..... D
AC ..... :arrow: ..... 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.
donger
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Hi Powerscore,

I'm preparing for the June LSAT and am taking Powerscore tutoring to help me do so.

I took preptest 43 and ran into a stimulus I didn't know how to quite diagram. Could you please help me out? The relevant sentence is: "If the soil's nutrients are completely depleted, additional crops cannot be grown unless fertilizer is applied to the soil." The trouble I had with this is that there is a sufficient condition and a necessary condition that is followed by a necessary condition. How would you diagram this?

Thank you!
Steve Stein
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Hi Donger,

That's an interesting twist on the standard "unless." We can still basically apply PowerScore's Unless Equation, though, recognizing the condition that follows the word "unless" as the necessary condition, and negating the other condition (additional crops cannot be grown):

Soil completely depleted
..... and ..... ..... ..... :arrow: fertilizer applied
Additional crops can be grown

On the contrapositive side, if fertilizer is not applied, then either the soil was not completely depleted or additional crops cannot be grown:

..... ..... ..... ..... ..... ..... soil not completely depleted
fertilizer not applied :arrow: or
..... ..... ..... ..... ..... ..... additional crops cannot be grown

I hope that's helpful! Let me know whether it's clear--thanks!

~Steve
Steve Stein
PowerScore Test Preparation
donger
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Ah, yes! It is clear now.

Thank you,
Donger
Barcelona10
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This is a Must Be True question I believe. I've read through this passage several times, and am still a bit confused as to how to find the correct answer. I see that there is conditional language involved in the first two sentences, and then I assume that the question is related to these sentences because the question refers to fertilizer, but I am stuck because I'm not sure how to symbolize the first two sentences which have both "If..then...unless".

Can you help me symbolize the first two sentences?
Steve Stein
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Hi Barcelona10,

Good question! That's a tough one. The first sentence provides that failing to rotate crops will deplete the soil unless other preventative measures are taken. In other words, if you fail to rotate the crops, and you don't take other preventative measures, the soil will be depleted:

NO Crop rotation
and ..... ..... ..... :arrow: soil depletion
NO preventative measures

...on the contrapositive side, if there is no soil depletion, we can be sure that either the crops were rotated or other preventative measures were taken:

..... ..... ..... ..... ..... ..... crop rotation
NO soil depletion :arrow: ..... ..... or
..... ..... ..... ..... ..... ..... preventative measures


The second sentence provides that in the case of complete depletion, additional crops can't be grown unless fertilizer is applied. In other words, if there is complete depletion, and fertilizer is not applied, additional crops cannot be grown:

complete depletion
and ..... ..... :arrow: NO additional crops
NO fertilizer

...and the contrapositive tells us that if additional crops can be grown, either there has not been complete depletion or there has been fertilizer applied:

..... ..... ..... ..... ..... NOT compete depletion
Additional crops :arrow: ..... or
..... ..... ..... ..... ..... Fertilizer applied

I hope that's helpful! Please let me know whether this is clear--thanks!

~Steve
Steve Stein
PowerScore Test Preparation
Barcelona10
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So, because we know that crops were grown, and no fertilizer was present, we know that the soil could not have been fully depleted---because according to conditional 2, if depleted and no fertizlier, then no crops grown. Is this logic sound, and the basis for C?

Also, in more abstract terms then, If A, then B, unless C, TRANSLATES to IF A and not C, then B?

Thank you so much for the response. Greatly appreciated.
Steve Stein
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Hey Barcelona10,

You are correct on both counts; that one's got some challenging conditional language...nice work!

~Steve
Steve Stein
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eober
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Hi,

I am a bit confused about answer choice C: "The vegetables were grown in soil that had not been completely depleted of nutrients but not necessarily soil in which crops had been rotated".

Rotate (not) :arrow: nutrients depleted

nutrients depleted (not) :arrow: measures taken

Is the answer choice just trying to say that it does not matter whether or not the rotation took place in a non-fertilized soil because the measures must have been taken given that (C) states that "in soil that had not been competely depleted of nutrient". Do I understand (C) correctly?

Thank you for the clarification!
Steve Stein
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Hi,

Thanks for your message--that's an interesting question, and you've got it almost exactly.

Based on the information provided by the author, the fact that vegetables were able to grow at all tells us that, at the very least, the soil's nutrients have not been completely depleted.

We can't say for sure whether the crops have been rotated, or whether any measure have been taken--we just know that if depletion that has taken place at all, it is not complete.

I hope that's helpful! Please let me know whether this is clear--thanks!

~Steve
Steve Stein
PowerScore Test Preparation