gmatbeater2007 wrote:In the years since the city of London imposed strict air-pollution regulations on local industry, the number of bird species seen in and around London has increased dramatically. Similar air-pollution rules should be imposed in other major cities.

Each of the following is an assumption made in the argument above EXCEPT:

(A) In most major cities, air-pollution problems are caused almost entirely by local industry.

(B) Air-pollution regulations on industry have a significant impact on the quality of the air.

(C) The air-pollution problems of other major cities are basically similar to those once suffered by London.

(D) An increase in the number of bird species in and around a city is desirable.

(E) The increased sightings of bird species in and around London reflect an actual increase in the number of species in the area.

The correct answer is A. I marked E.

Why would the correct answer be A? In fact it sounds like an strong assumption.

Any thoughts?

Try negating Answer choice A and see if that destroys the argument. Because if it is an assumption then negating it would mean the argument can no longer be valid.

So A says:
In most major cities, air-pollution problems are caused almost entirely by local industry.

Now negate the above:
In most major cities, air-pollution problems are not caused almost entirely by local industry.

If air pollution is not entirely caused by the local industry does that destroy the argument. Not really. It just says that other factors could be responsible for the pollution. The author can still claim that pollution from the local industry claims to be having a negative effect on birds (as it could be one of those many factors responsible) and regulations on the industry would remove that effect. Clearly it does not hurt the argument when negated infact it does not do anything to the argument. So its not an assumption made by the author hence the right answer.

Now negate the answer choice E:
The increased sightings of bird species in and around London does not reflect an actual increase in the number of species in the area.

If the sightings does not reflect an actual increase then there is no reason to believe that the regulations played any role in this situation. Infact the sudden increase in the number of species of birds could be due to other factors - changing weather patterns around the world etc. Hence if the regulations are not helpful then the author cannot conclude that such regulations are needed in other major cities too. Clearly negating this statement destroys the argument hence it is an assumption and the wrong answer choice.