Urban air contains more sulfur dioxide than does rural air

[gmat_s]

Please let me know what is the reasoning behind this answer:

Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas. In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide. Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Which of the following, if true, would it be most important to take into account in evaluating the result?
A. The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas.
B. At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.
C. The urban class conducting the experiment was larger than the rural class conducting the experiment.
D. Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside.
E. Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school's greenhouse were changed more frequently than were those at the rural school.

Source: GMAT Prep Test 1, OA is D

[Harish Dorai]

If you look at the sentences, we can infer that Sulphur Dioxide is considered as the main culprit for the slow growth of the plants and the experiments were done to find the extend of damage done by Sulphur Dioxideand see how much of a growth difference in growth is brought in. The results shows that the urban plants grew more slowly than rural plants. So if we analyze the experimental results, there is something else other than Sulphur Dioxide that contributed for the slower growth.

So what we need to consider is anything other than Sulphur Dioxide that could hinder the growth of the plants. So the answer choice should be something that is not related to Sulphur Dioxide, which is causing the slow growth.

A) It says Sulphur Dioxide level was lower at the urban school. But still the urban plants grew slower. So this choice, give support to the argument that there is something else other than Sulphur dioxide that contributed to the slower growth. But it doesn't give any hint on what else could have caused the slow growth.

B) This choice compares Open urban plants vs. Greenhouse Urban plants and similarly for the Rural plants. But it doesn't provide an alternate reason for the slow growth.

C) Size of the urban class is no way related to the slower growth of plants.

D) This gives an alternate reason for the slow growth. Urban greenhouses prevented enough sunlight to reach the plants and hence it caused a slower growth.

E) This statement though says that the filters were replaced frequently, it is difficult to figure out an alternate reason for the slow growth.

So (D) seems be a more appropriate answer.

[dbernst]

Harish, thanks for the well-reasoned explanation. I simply wish to add a few points.

The argument states that even in greenhouse environments where sulfer dioxide was entirely eliminate the urban plants grew more slowly than the rural plants. This seems to indicate, as Harish states, that some other factor appears to account for the difference in growth rates between urban and rural plants, at least within the greenhouse environment.

A. This choice is irrelevant, since both the urban and rural greenhouses are free of sulfur dioxide.
B. This choice doesn't account for any difference in growth; instead, it indicates that the greenhouse environments in both urban and rural areas are more conducive to plant growth than are the outside environments.
C. Irrelevant. Size of class does not matter.
D. This answer choice provides a factor other than sulfer dioxide that may account for the slow growth in urban environments. This is important because it undermines certain potential conclusions that the classes might make concerning the relationship between sulfer dioxide and plant growth in urban and rural environments.
E. Irrelevant. Both environments still remained sulfer dioxide free.

gmat_s, I do have something to add: I don't think that D is a perfect answer, but it is the best of the bunch. This is a major challenge on the GMAT Verbal, particularly for students who are used to selecting provably correct answers. On Verbal, and especially on CR and RC, you cannot mathematically prove the answer correct. Instead, you can only demonstrate why one answer is better than the others.

Hope that helps.
-dan

Please let me know what is the reasoning behind this answer:

Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas. In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide. Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Which of the following, if true, would it be most important to take into account in evaluating the result?

A. The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas.
B. At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.
C. The urban class conducting the experiment was larger than the rural class conducting the experiment.
D. Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside.
E. Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school's greenhouse were changed more frequently than were those at the rural school.

Source: GMAT Prep Test 1, OA is D

[fenruyun]

D. This answer choice provides a factor other than sulfer dioxide that may account for the slow growth in urban environments. This is important because it undermines certain potential conclusions that the classes might make concerning the relationship between sulfer dioxide and plant growth in urban and rural environments.

Please let me know what is the reasoning behind this answer:

Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas. In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide. Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Which of the following, if true, would it be most important to take into account in evaluating the result?

A. The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas.
B. At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.
C. The urban class conducting the experiment was larger than the rural class conducting the experiment.
D. Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside.
E. Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school's greenhouse were changed more frequently than were those at the rural school.

Source: GMAT Prep Test 1, OA is D

I don't understand. Even if the situation mentioned in D really exists, it doesn't mean that there's no relationship between sulfer dioxide and plant growth in urban and rural environments. The experiment can simply prove that besides sulfer dioxide,there's other factors that may affect the plant growth in urban and rural environments.

I don't quite get it. What does this argument try to put. It first raised an question: how much of the difference in growth is due to sulfur dioxide.Then somebody conducted an experiment,which showed that the plant still grows slower in the greenhouse environment in urban area even if the two environment are both clear out of sulfer dioxide. Then it asks us to evaluate the result.
So, how should we evaluate. Like what I have said,The experiment can simply prove that besides sulfer dioxide,there's other factors that may affect the plant growth in urban and rural environments.

It could be much clear if this problem simply ask us to explain the result rather than evaluate it.

Can somebody explain this ? Thank u !

[RonPurewal]

The experiment can simply prove that besides sulfer dioxide,there's other factors that may affect the plant growth in urban and rural environments.

that's the whole idea: sulfur dioxide vs. other factors. if you can prove that there are other factors at work, then you are showing that sulfur dioxide plays less of a role.

* if there are differences in the amount of light being let through the windows, then the experimental control (identical conditions) is destroyed, and it's still possible that sulfur dioxide causes the urban/rural difference.
* if there are NOT differences in the amount of light, then, since all the sulfur dioxide is sucked out of the greenhouses, the difference MUST be caused by other factors.

(d) will determine this difference.

--

most importantly:
which choice did you think was better than (d)? and why?

[pradeepchandy]

I had a minor doubt (since we are asked to read CR literally)

"classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide. "

How do we know that they did not use plants to filter out S02 ?

By sentence correction rules , the first clause can lead to the second clause

[sangeethmani]

I get your point when you need to strengthen the argument.

As this is an evaluate question.. If the answer was no.. How does it weaken the argument that something else other than SO2 didn't cause the intended growth in plants. Do u mean to say this is the only cause which could have got the effect?

[sangeethmani]

What about b? When u ask a question to yourself and answer it with a yes or no in the case of B.
Then with a 1. Yes: Maybe So2 was retarding the growth of the plants.(weakens the argument)
2. No. then there maybe other factors responsible(strengthens the argument)..

Please help!

[mschwrtz]

What about b? When u ask a question to yourself and answer it with a yes or no in the case of B.
Then with a 1. Yes: Maybe So2 was retarding the growth of the plants.(weakens the argument)
2. No. then there maybe other factors responsible(strengthens the argument)..

Please help!

Excellent question. If the question were Does So2 retard growth? then B would be more helpful in evaluating the results. Even then, though, it wouldn't be a great answer, because we wouldn't know that the presence of So2 was the reason for the greenhouse/outside difference. Even in your own account you used maybe twice.

And the real question is How much of the difference in growth (between urban and rural areas) is due to So2? The greenhouse experiment is supposed to control for So2, but leave other relevant differences. D suggests that the greenhouse experiment in fact created confounding differences.

[abhishek.gpta]

Sorry but bumping this but I have a doubt regarding the answer D.

Even though my gut told me D is the best, it was based on my personal knowledge that lightning affects plant growth so going with textbook concepts and assuming nothing on my own, I went with my second choice A, which is incorrect.

How do I choose the correct answer in such scenarios?

[RonPurewal]

going with textbook concepts and assuming nothing on my own, ...

if your way of approaching strengthening/weakening/evaluating questions is to "go with textbook concepts and assume nothing on [your] own", then you are going to be in big trouble. essentially ALL strengthening/weakening/evaluating questions require some modicum of common sense and/or real-world intuition. just scan a handful of OG questions and this will be patently clear.

you won't need any specialized knowledge, but, if it's anything that most grade-school kids would know, then you may be called upon to use it.
e.g.,
"plants need light to grow" (here)
"tall buildings are usually built in cities, where land costs more" (OG13 #94)
"if people know they'll probably be caught, they will be less likely to do bad things" (OG13 #110)
etc.

in fact, this is the whole point of these problems! the main purpose of these problems is to eliminate candidates who only think with "formal logic" or "textbook concepts".
keep that in mind when you are evaluating them.

[abhishek.gpta]

Thanks for clarifying Ron, much appreciated.

[tim]

:)

[mcmebk]

I have been tossing around between B/D.

As for B, my thinking process is: Comparing with plants planted outdoors, plants within the greenhouse grow in a SO2 free environment. The fact that both of the plants grow much more quickly than those planted outside give a strong evidence that "SO2 causes a big difference in growth."

Imagine a different scenerio, they grow more or less at the same rate as plants planted outside, then eliminating SO2 has very little effect on the growth. We can think of other scenerios as well, say the difference between plants grown inside and outside of greenhouse in rural school is not as great as the difference in urban school, then it is an evidence that removing SO2 helps the growth in urban city more because of the higher content of SO2 in the air, to help to deduct that SO2 does affect the growth very noticeably...

As for D, it is unclear to me how it helps to evaluate the result:
Now that plants in urban area and rural area are both grown in a condition that the effect of SO2 has been eliminated, the result that those plants still grow at a different rate surely indicate a certain thing that some other factors, besides SO2, is affecting the growth rate. Option D merely gives one example for a long list of possible factors (temperature, pressure, amount of plants....) but that won't help to determine the effect of SO2.

To go even further, lights can have positive or negative effects on plants; some plants grow slowly when there is not sufficient light while there are some plants flourishing in a shadowed environment, that seems to give us another reason not to choose D.

I am having trouble with CR, not knowing if I should just let my mind flow in GMAT's logic way, forcing myself to accept the right answer, or I should stick to my own thinking and try to defend for myself, in which case I may enhance my GMAT-wrong thinking capability.

Please help.

[RonPurewal]

As for B, my thinking process is: Comparing with plants planted outdoors, plants within the greenhouse grow in a SO2 free environment. The fact that both of the plants grow much more quickly than those planted outside give a strong evidence that "SO2 causes a big difference in growth."

... right, but that's not the point here; the point is to account for the difference between the results observed in rural and urban areas.

Imagine a different scenerio, they grow more or less at the same rate as plants planted outside, then eliminating SO2 has very little effect on the growth. We can think of other scenerios as well, say the difference between plants grown inside and outside of greenhouse in rural school is not as great as the difference in urban school, then it is an evidence that removing SO2 helps the growth in urban city more because of the higher content of SO2 in the air, to help to deduct that SO2 does affect the growth very noticeably...

this is all fairly perceptive -- but, unfortunately, it doesn't really pertain to the answer choices given here.

Option D merely gives one example for a long list of possible factors (temperature, pressure, amount of plants....) but that won't help to determine the effect of SO2.

... but it's still something that could account for the observed difference, and that's all that matters.

the argument you're making here amounts to, essentially, "this doesn't prove that sunlight is the issue". no, it doesn't conclusively prove that -- but it doesn't have to. it just has to be something else that could reasonably account for the observed phenomenon.

To go even further, lights can have positive or negative effects on plants; some plants grow slowly when there is not sufficient light while there are some plants flourishing in a shadowed environment, that seems to give us another reason not to choose D.

all plants growing on the surface of the earth need sunlight. every single one of them.