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Bunuel
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This question is tricky took me 3.50 mins to figure out....

so most of people were trapped in choose the option E.

E Regions that are geographically closest are most likely to be affected in similar ways.

THINK, THINK, THINK if regions that close to each other will be affected in the same pattern? wait...a sec... didn't the question just mentioned it is a random pattern? gotcha tempting tho but it actually weakens the conclusion. hope my explanation helps.
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can someone post the OA to this?
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Temperature shifts can trend toward warming or cooling, based on a number of gravitational, seasonal, and human variables. These variables affect different ecosystems differently and thus should produce a random pattern in which some ecosystems warm while others cool. However, data gathered in a 1980s study shows that the shifts occur in a definitely skewed pattern, with most areas’ temperatures rising simultaneously.
We have to explain the paradox that various variables affect ecosystems differently and thus produce random pattern of warm and cool climate over these ecosystems. However data from 1980 shows that temperature increased in skewed pattern in different ecosystems
A Massive warming can result from widespread pollution in many countries.- External variable which explains the paradox, keep it.

B Certain regions with specific geographical features respond in varying degrees to surrounding changes.- Doesn't resolve the paradox as it mentions the effect of surroundings on the geographical regions with their specific features but we have to explain the reverse. Discard it.

C Some regions grow warmer due to increased volcanic activity in those regions.- For some region temperature increase is there due to volcanic eruption but the statement that conditions are skewed over different ecosystems is still not resolved. Most ecosystem don't have volcanic eruption so why are conditions skewed there as well.

D In the 1990s and beyond, which were not as well documented, human pollution skewed the trend toward warming.- premise discuss about data collected in 1980 but the option discuss about 1990 and that too undocumented, however at first go option seems similar to A but can be discarded as paradox is not resolved regarding the data collected in 1980.

E Regions that are geographically closest are most likely to be affected in similar ways.- This also seems a contender to resolve the paradox but the original statement mentions that various ecosystems shows random pattern depending upon various variables.

Therefore A is the correct answer

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There seems to be a lot of discussion on this question, so I will try my best to help out:

A) This is a good choice. If there is one variable that can influence a large number of areas, then it might explain why, despite the seemingly random nature of temperature, there was an increase across all areas - because of pollution influencing all the areas in the study.

B) This is simply restating what was already said in the passage. The passage says "These variables affect different ecosystems differently", so B is just repeating information.

C) In a similar fashion to A, this tries to give a variable that is common across all the regions studied. Howeverr, the phrasing of the answer makes it a weak choice - it says "some areas have volcanos.." What about the other areas without volcanos? Why would their temperature increase? C is therefore a much weaker option than A.

D) Trap choice. The study in question occurred in the 1980s. If the study occured in the 80s, how would it have known what would happen in the 90s?

E) This is the one most people select. Frankly, it is not a terrible choice - except it requires one very crucial assumption that is not given in the passage: the areas in the study are "geographically close". Read the passage carefully. All that is known is that areas have temperatures that increased at the same time. There is nothing stated if the areas are geographically similar or not. What if one area in the study was in Japan and the other in Iceland? There is no way to determine with the given information what the geography of the areas used in the study was, so E cannot be the correct choice without further information.

That leaves the answer choice A, which is the correct answer.
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But A talks about countries and the question is about ecosystems right?
mysterymanrog
There seems to be a lot of discussion on this question, so I will try my best to help out:

A) This is a good choice. If there is one variable that can influence a large number of areas, then it might explain why, despite the seemingly random nature of temperature, there was an increase across all areas - because of pollution influencing all the areas in the study.

B) This is simply restating what was already said in the passage. The passage says "These variables affect different ecosystems differently", so B is just repeating information.

C) In a similar fashion to A, this tries to give a variable that is common across all the regions studied. Howeverr, the phrasing of the answer makes it a weak choice - it says "some areas have volcanos.." What about the other areas without volcanos? Why would their temperature increase? C is therefore a much weaker option than A.

D) Trap choice. The study in question occurred in the 1980s. If the study occured in the 80s, how would it have known what would happen in the 90s?

E) This is the one most people select. Frankly, it is not a terrible choice - except it requires one very crucial assumption that is not given in the passage: the areas in the study are "geographically close". Read the passage carefully. All that is known is that areas have temperatures that increased at the same time. There is nothing stated if the areas are geographically similar or not. What if one area in the study was in Japan and the other in Iceland? There is no way to determine with the given information what the geography of the areas used in the study was, so E cannot be the correct choice without further information.

That leaves the answer choice A, which is the correct answer.
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