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.

OA is [spoiler]D[/spoiler]. Please explain.

Theory: In environments containing sulfur dioxide, plants grow slower than in environments without (or with less) sulfur dioxide.

Experiment: Filter sulfur dioxide from the air drawn in to urban and rural green houses, and observe plant growth rates in each.

Implied expectation: Plants should grow at the same rate in both greenhouses.

Observation: Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Logical conclusion: Something other than sulfur dioxide must have retarded plant growth in the urban greenhouse.

Therefore C is the best answer because it provides another factor that could explain the observation.

A,B,C are eliminated quickly as they are beyond scope.

between D and E,

E states that more sulphur di oxide is their in urban area.
this is essentially a restatement of the premises.

D gives an alternate reason,which if true must be used in determining the size of the plants.

hence D it is.

I think it is a clear "B". What is the original answer btw?

Sulphur dioxide is not in question here. It was already filtered out from the greenhouse. We are trying to assess if sulfur dioxide is the main reason. Consider "B"

Now sulfur dioxide emissions occur at both places, more in urban than rural areas. Plants growing outside the greenhouses grew much slower, they were exposed to the sulfur dioxide. The plants in the greenhouses weren't and they grew much faster. Since there was no sulfur dioxide. THere could be other reasons why plants grew faster in the rural areas but that is not what we are concerned about. We are trying to find out if cutting sulfur dioxide from the environment, boosts their growth. And it happens without fail in both cases. The experiment still provided enough information to conclude that. So this must be taken into account.

Hence "B" should be the answer.

IMO D

the conditions should be similar at both locations for verifying whether Sulphur dioxide has any effect on their growth. if at one location it accumulates any grime and blocks sunlight, the conditions are not identical. hence it should be taken into account.

user123321

chieftang wrote:Theory: In environments containing sulfur dioxide, plants grow slower than in environments without (or with less) sulfur dioxide.

Experiment: Filter sulfur dioxide from the air drawn in to urban and rural green houses, and observe plant growth rates in each.

Implied expectation: Plants should grow at the same rate in both greenhouses.

Observation: Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Logical conclusion: Something other than sulfur dioxide must have retarded plant growth in the urban greenhouse.

Therefore C is the best answer because it provides another factor that could explain the observation.

Sorry, I did mean to give D as the answer, not C. That should be obvious after my explanation.

chieftang wrote:Theory: In environments containing sulfur dioxide, plants grow slower than in environments without (or with less) sulfur dioxide.

Experiment: Filter sulfur dioxide from the air drawn in to urban and rural green houses, and observe plant growth rates in each.

Implied expectation: Plants should grow at the same rate in both greenhouses.

Observation: Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Logical conclusion: Something other than sulfur dioxide must have retarded plant growth in the urban greenhouse.

Therefore C is the best answer because it provides another factor that could explain the observation.

Sorry, typo above. I did mean to give D as the answer, not C. That should be obvious after my explanation.