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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:

Often the words in CR questions encourage us to bring outside knowledge to the question. We might think, when reading the above, 'of course air pollution is bad, and should be reduced', and this might lead us to ignore the structure of the argument. The argument says, essentially, "London imposed air pollution laws. The number of birds went up. Therefore the rules should be applied everywhere."

When I see an argument like this, I'll normally replace, in my head, the words with letters. The argument is: "London did X. The number of Y went up. Therefore every other city should do X." Now the argument's structure is clear; the fact that Y went up is the justification for implementing X.

In the original argument, what is the justification for the conclusion? Precisely that there were more birds. It's an unstated assumption that having more birds is a good thing; it's the only justification for improving air quality that is provided. So D is one of the assumptions. That we should apply London's rules elsewhere assumes other cities are similar: C is an assumption. That the increased sightings of birds actually represents an increase in the number of birds is another assumption: E is also assumed.

B is not an assumption explicitly made in the argument. I suppose it's possible that air pollution regulations led to more birds for a different reason than by improving air quality, but that seems far-fetched. Still, if no other answer were good, this would be the choice. A, however, is clearly not assumed in the argument. The argument does not assume that local industry is 'almost entirely' the source of air pollution. It only assumes that regulation on local industry will have a positive effect.

Incidentally, there aren't many birds in London!

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(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.

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