Two centuries ago, Tufe Peninsula became separated form the mainland, isolating on the newly formed Tufe Island a population of Turfil sunflowers. This population’s descendants grow to be, on average, 40 centimeters shorter than Turfil sunflowers found on the mainland. Tufe Island is significantly drier than Tufe Peninsula was. So the current average height of Tufe’s Turfil sunflowers is undoubtedly at least partially attributable to changes in Tufe’s environmental conditions.

Which of the following is an assumption on which the argument depends?


(A) There are no types of vegetation on Tufe Island that are known to benefit from dry conditions.

(B) There were about as many Turfil sunflowers on Tufe Peninsula two centuries ago as there are on Tufe Island today.

(C) The mainland’s environment has not changed in ways that have resulted in Turfil sunflowers on the mainland growing to be 40 centimeters taller than they did two centuries ago.

(D) The soil on Tufe Island, unlike that on the mainland, lacks important nutrients that help Turfil sunflowers survive and grow tall in a dry environment.

(E) The 40-centimeter height difference between the Turfil sunflowers on Tufe Island and those on the mainland is the only difference between the two populations.

conclusion: changes are attributable to Turfe's environmental changes

evidence1: sunflower 40cm shorter than on the mainland
evidence": Tufe Island is dryer than mainland was 200 years ago

assumption: only the island's climate has changed

A. irrelevant
B. irrelevant
C. The mainland’s environment has not changed, best answer
D. argument is about climate and not nutrients
E. can not be assumed

Facts
-Two centuries ago, Tufe Peninsula became separated form the mainland isolating on the newly formed Tufe Island a population of Turfil sunflowers
-This population’s descendants grow to be, on average, 40 centimeters shorter than Turfil sunflowers found on the mainland
-Tufe Island is significantly drier than Tufe Peninsula was
Conclusion
- So the current average height of Tufe’s Turfil sunflower is undoubtedly at least partially attributable to changes in Tufe’s environmental conditions

Now let's look at the options
A - Eliminate - Out of scope.
B - Eliminate - Out of scope.
D - Eliminate - More of a fact than an assumption.
E - Eliminate - More of a fact than an assumption.

C - Correct - Is an assumption - It says that the mainland’s environment has not changed so there is no change in the height of the Turfil sunflowers on the mainland. Hence the difference in the height is only due to the change in the island's environment.

This goes with the conclusion.

Hence C should be the answer.

By stating "The soil on Tufe Island, unlike that on the mainland," choice D is implying that the soil in the Tufe Peninsula is causing the Turfil to grow taller rather than the conclusion we are trying to strengthen - changes in the environment between the two land masses. Thus we are not strengthening the argument.

Additionally, a great tactic to employ with assumption questions, one I find used frequently in posts, is the negation technique. If we negate Choice D by saying that the soil HAS important nutrients rather than LACKS important nutrients does this negation of the assumption destroy the case being made in the argument that it's the environment's fault? Not really. The flowers can possibly have the important nutrients to grow taller, maybe 5 cm, and still be shorter as a result of the dry environment. Whereas in choice C if we negate the answer choice by saying "The mainland's environment HAS changed..." then we destroy the conclusion by saying that it's not the drier environment that caused the flowers to shrink but the better environment that caused them to grow.

Hi Nitin,

Is soil the only component of environment which can impact plant growth?

What about temperature, humidity etc? These can also impact plant growth. Right?

Now, even if the soil does not lack such nutrients, one of these other factors (temperature, humidity) could still be responsible for the difference in the heights of the flowers.

In such a case, the conclusion does not break down.

Isn't it?

When you negate an assumption, the conclusion should break-down. Right?

So, your job should be to find a scenario in which the conclusion could still hold true. Only in case where you are not able to find such a scenario can you confidently say that the conclusion has actually broken down. In such a case, the option statement is an actual assumption.

Does it help?

Feel free to ask if you have any further questions

Thanks,
Chiranjeev
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Dear Umesh,

Thank you for your query.

After going through your analyses of choices C and D, I feel that you are not asking yourself the right questions in the pre-thinking phase.

Accordingly, let's see where you may be faltering in applying the process.

Right now we are given three things, as you have rightly pointed.
1. Separation of the peninsula from the mainland
2. Difference in the environmental conditions between the peninsula and the island
3. Difference in the height of the sunflowers found on the island and those found on the mainland

On the basis of the above three facts, the author concludes that the difference in the environmental conditions between the peninsula and the island is responsible at least to some extent for the current (shorter) average height of the sunflowers found on the island. Now, in the pre-thinking phase for assumptions, what do we focus on? We try to think of scenarios in which the conclusion may not hold, right? Accordingly, what if someone told you that the difference in the height is not because the island sunflowers are shorter than before but because the mainland sunflowers are taller than before because of the changes in the environmental conditions on the mainland? Would the author's conclusion still be valid? Would the author still be able to blame the difference in the environmental conditions between the peninsula and the island as the cause for the difference in the average height of the sunflowers found at the two different places? The answer is NO! Choice C rules out this possibility by negating a possible counter to the link drawn between the difference in the environmental conditions between the peninsula and the island, and the difference in the height of the sunflowers. Try to negate Choice C and see the effect it has on the conclusion.

As regards choice D, ask yourself whether it is a must be true statement for the conclusion to hold true? Chiranjeev has addressed a similar doubt above. Please do present your analysis in the light of that discussion and we'll take our discussion forward from there.

Regards,

Neeti.
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Lets try-



The last sentence ( The conclusion ) of the stimulus is very important, it says everything the author wants to convey.

Now lets decode the authors reasoning.

Mainland - Height of Plant is H
Island - Height of Plant is H - 40

Now carefully check the last to sentences ( more closely on the green part ) which leads to the conclusion.



This clearly means that change in environmental conditions ( Environment of the island becoming drier) may be one of the reasons ( There may be other factors as well) that have resulted in reduced height of the sunflowers in the island.

Lets check the option (A) -

A. There are no types of vegetation on Tufe Island that are known to benefit from dry conditions.

We do not have sufficient information to state whether any type of vegetation benefits or not , further it is doubtful what the term benefits exactly mean ( Does increase in height constitute as a benefit or something else)

Hence IMHO (C) is a better option, and if we negate the option the entire argument falls apart.
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No, actually the other way round. The island plants grow 40 cm less than the mainland plants. However the point is not which group grows more - it is the difference in growth that matters:

There are 3 environmental conditions discussed here:

1. Past: the environmental condition of the mainland (the island was a part of the mainland then).
2. Present: the environmental condition of the mainland.
3. Present: the environmental condition of the island.

The argument is:
Present: the plan height on island is different from plant height on main land ( the plants under conditions 2 and 3 are different).
However the reason for this difference is stated as the difference between 1 and 3 ( NOT 2 and 3!)... "Tufe Island is significantly drier than Tufe Peninsula WAS". So it is assumed that condition 2 has not changed in the same way as condition 3.

Another approach (negation):

The mainland’s environment has not changed. Thus the conditions 2 and 3 are same now, so there is no environmental reason that the heights would be different. Thus the argument breaks down.

Option C is hence correct.

The confusion in this question is basically down to how the conclusion is formulated:



The conclusion is: So the current average height of Tufe’s Turfil sunflowers is undoubtedly at least partially attributable to changes in Tufe’s environmental conditions.

The conclusion actually says : So the current average height of Tufe’s Turfil sunflowers is undoubtedly at least partially attributable to changes in Tufe’s environmental conditions. [WHAT CHANGES? Tufe Island is significantly drier than Tufe Peninsula was.] [Note: It is important to understand that this is the only change that is in the scope of the question. Any other reasons/agents of "change" is out of scope].

So it assumes that the fact that "Tufe Island is significantly drier than Tufe Peninsula was" plays an undefined (tiny or large) role in this situation.

Option C expressly omits an alternate explanation that would, if true, render this conclusion worthless.

C. The mainland’s environment has not changed in ways that have resulted in Turfil sunflowers on the mainland growing to be 40 centimeters taller than they did two centuries ago.

This would mean that the drier climate in the Island (vs. 2 centuries ago) played absolutely NO part (small or large). This is the key link between the premise and the conclusion and is therefore the correct answer.