Thus the burden of pollution such older United States automobiles contribute to the [color=#804000]global atmosphere will be gradually reduced over the next decade[/color].

Thus we need to look for statement where it shows, pollution from any other geo
Which one of the following, if true, most seriously weakens the argument?


(A) It is impossible to separate the air of one country or jurisdiction from that of others.-irrelevant, eliminate
(B) When automobiles that are now new become older, they will, because of a design change, cause less air pollution than older automobiles do now.-> irrelevant, eliminate it

(C) There is a thriving market for used older Untied States automobiles that are exported to regions that have no emission-control regulations.-> the vehicles will continue to pollute from a different country, sounds good, hold it!

(D) The number of jurisdictions in the United States requiring automobiles to pass emission-control inspections is no longer increasing.->irrelevant, eliminate it

(E) Even if all the older automobiles in the United States were retired from service, air pollution from United States automobiles could still increase if the total number of automobiles in use should increase significantly.->irrelevant, eliminate it.

Thus C
_________________

Persistence+Patience+Persistence+Patience=G...O...A...L

I will go with C.

(A) It is impossible to separate the air of one country or jurisdiction from that of others.-irrelevant, eliminate.
Main topic does talk about global phenomenon, but it does not talk about jurisdiction in other countires.

(B) When automobiles that are now new become older, they will, because of a design change, cause less air pollution than older automobiles do now
If true, this will strenthen the argument rather than weaking it so eliminate it.

(C) There is a thriving market for used older Untied States automobiles that are exported to regions that have no emission-control regulations.
Seems good. As although vechiles were taken off the US roads but if they are used in some other countries, then these old vechiles will continue to add to global pollution. So taking off from US road is not helping to ease off the pollution.

(D) The number of jurisdictions in the United States requiring automobiles to pass emission-control inspections is no longer increasing.
Number of jurisdiction has nothing to do with emission control. It may be already the case that whole of US is covered by these jurisdictions so there is no need to increase the jurisdictions.

(E) Even if all the older automobiles in the United States were retired from service, air pollution from United States automobiles could still increase if the total number of automobiles in use should increase significantly.
Seems good, however as newer vechiles may be technologically advance and may contribute very less compared to old vechile so increased number may not add upto the pollution. So it can be ruled out.

C it is.
We are talking about global pollution..so if those cars are still used somewhere ..means we are still polluting the globe...

E is actually relevant to the conclusion: after all, if E is actually true, it could undermine the conclusion.

However, the problem with E is due to the conditional language: it says if number of older car increases, then pollution will increase. Well,
does the stimulus actually say that number of older car is increasing? Nope.
Thus, E is wrong because it requires additional assumption, that the number is car is increasing.

C, on the other hand, is just a clear-cut answer, requiring no additional assumption: the stimulus says that older car contributes to air pollution and if they are sold to markets where there is no test, then yes, decrease in air pollution won't seem likely.