Critical Reasoning

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.

[spoiler]OA: Later[/spoiler]

Would any one explain how to tackle these kind of CR's?
Thanks.

D is correct by POE

I find D to be the only correct explanation.

As if the grime deposits and lesser light can get through then plants are likely to grow slow.

Therefore my answer is D

Is there any YES/NO rule to eliminate the wrong answers?

Is it an evaluation type question?

Thanks.

I think this is moreover scope question. If you understand scope properly then this question is easy. Because other than D, I feel all other are out of scope

gmat_perfect wrote:Is there any YES/NO rule to eliminate the wrong answers?

Is it an evaluation type question?

Thanks.

My answer choice was based on the fact that growth of plants depends on many factors and not just presence or absence of a pollutant which is sulphur dioxide.

So i was just simply looking for an answer choice that would point out something else that is responsible for growth of plants.
And grime pointed out less light getting through.