Although air pollution was previously thought to exist almost exclusiv

Question

Although air pollution was previously thought to exist almost exclusively in our nation’s cities, the recent increase in the number of persons suffering from illnesses attributed to excessive air pollution leaves us no choice but to conclude that other, nonurban areas are now affected.

Which of the following, if true, would most seriously weaken the conclusion of the argument above?

(A) The nation’s cities have seen a marked decrease in levels of air pollution.

(B) The nation has experienced a sharp decrease in the number of people moving out of its cities.

(C) Illnesses due to air pollution are among the least common causes of death to urban dwellers.

(D) Many illnesses previously thought unrelated to air pollution are now considered to be caused by it.

(E) As a result of the problems in urban areas, nonurban areas have passed strict pollution control measures.

aritrar4 · Answer

A. If cities have seen a decrease in air pollution level, that doesn't weaken our case. It is either a strengthener or neutral at best.

B. This isn't related to our argument, since deals with the disease of people living in the city. If fewer people are moving out of the city, that might spike the disease in cities only and not the non-urban areas.

C. This is irrelevant since we are not concerned with deaths, but just the disease affecting people.

D. This is a weakener since, more diseases are being attributed to air pollution than before. So previously if people suffered from a disease that was thought to have some other cause, now the cause of the disease is identified as air pollution. So it doesn't mean that air pollution has increased considerably.

E. This is again unrelated since passage of pollution control laws is not relevant to actual increase in air pollution.

IMO - option D

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Sumi1010 · Answer

Premise - The recent increase in the number of persons suffering from illnesses is attributed to excessive air pollution.
Conclusion - The non urban areas are  now  affected with air pollution.

Prethink - The conclusion relies on the number of person suffering from illness. 
Assumption - The recent increase in the number of persons suffering is  primarily due to  the illness of non-urban people.
 
To weaken the argument's conclusion, we should look for the choice that goes against this assumption.

(A) The nation’s cities have seen a marked decrease in levels of air pollution.
 The conclusion relies on the increased number of person suffering from illness. 
If cities have seen a marked decrease in levels of air pollution and we are sure that there is an excessive air pollution, we must believe that the air-pollution affected the non-urban areas. Strengthen the conclusion.  
(B) The nation has experienced a sharp decrease in the number of people moving out of its cities.
 The premise says about the total increase in the number of persons suffering from illness. 
This option actually just says that the number migrating outside the cities is much lesser (but still the total got increased). Hence,the number increased either within the city or non urban areas. Nothing else can be concluded.  
(C) Illnesses due to air pollution are among the  least common  causes of death to urban dwellers.
 The  severity  of illness is not a concern.  
(D) Many illnesses previously thought unrelated to air pollution are now considered to be caused by it.
 It actually says that the the increase in the number might not be actually because of excessive pollution but because of the way the cause was considered. Weakens the cause of the conclusion that non urban areas are  now  affected with air pollution. 
(E) As a result of the problems in urban areas, nonurban areas have passed strict pollution control measures.
 What happened to the measures? did they succeed? We don't know. We can't comment the current situation of non-urban areas.

IMO  D

ananya3 · Answer

P1: air pollution was previously thought to exist almost exclusively in our nation’s cities
P2: the recent increase in the number of persons suffering from illnesses are attributed to excessive air pollution 
Conclusion: nonurban areas are now affected.

pre-think: Increase in the number of reported cases attributed to air pollution => nonurban areas are now affected?

(A) The nation’s cities have seen a marked decrease in levels of air pollution. -  Incorrect 
This goes against the premise

(B) The nation has experienced a sharp decrease in the number of people moving out of its cities. -  Incorrect 
The premise #2 mentions that the number of people suffering has increased but does not mention anything about the area in which the increased number is coming from. Therefore even if this is true and fewer people are moving out of the city the overall number is still increasing and the argument still holds.

(C) Illnesses due to air pollution are among the least common causes of death to urban dwellers. -  Incorrect 
Out of scope. The argument is mainly concerned with illness related to air pollution

(D) Many illnesses previously thought unrelated to air pollution are now considered to be caused by it. -   Correct  
If this is true then the conclusion is wrong in saying that the nonurban areas are  now  affected. The people in the nonurban areas may have been affected a long time ago but their illness could have recently been attributed to air pollution

(E) As a result of the problems in urban areas, nonurban areas have passed strict pollution control measures. -  Incorrect 
Irrelevant. Was this done after the nonurban areas were affected? If true the conclusion will still hold. Moreover, the argument uses the increased number of cases as a basis to claim that nonurban areas are affected. This option does not explain anything with regards to the number

thereisaFire · Answer

Hi  VeritasKarishma   GMATNinja

I have a doubt in Choice B:

If the number of people leaving the cities decreases, then we can say " increase in the number of persons suffering from illnesses attributed to excessive air pollution " can be due to the increased number of people staying in the cities.

Let's say, there were 500 people in the cities with the migration rate X. After migration the number of people is 400. However, if the migration rate is X/2, then the strength of city dwellers after migration would be 450, more than when the migration rate was X. 
Since more people are now exposed to the polluted air in the city, this   increased number of people in the city   can be the reason for   increase in the number of people suffering from illnesses   attributed to excessive air pollution

Hence, it weakens the conclusion that the " nonurban areas are now affected "

Please help me in understanding where I am faltering.

KarishmaB · Answer

Yes, I agree. I did park this option on the side after reading it. It wasn't perfect but it did make some sense. The reason I wasn't happy with it is that if people are staying put in cities, the number of cases shouldn't increase. Is there some cycle that lots of people come in and lots go out of urban areas routinely and hence they spend only limited time there? We don't know. What happens normally is that people move to urban areas looking for jobs hence there is usually an influx. So this option didn't seem very well thought out but nevertheless did lead to some weakening of the conclusion.

Of course, after reading (D) it was clear that (D) is the answer and (B) is just a bad option.

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