Older United States automobiles have been identified as contributing

adkikani , just to add a bit to pikolo2510 's incisive answer. . .

I'm interested to see that E seems so tempting. Whether people are torn between C and E or just prefer E, the common theme is that E undermines the conclusion.

Not really.

I can see why people may think it does. Option E seems to have the cues that many methods train us to find.

Option E does address the issue of the old vehicles. It does contain the words "pollution" and "increase" and the phrase "U.S. automobiles."

On the other hand, superficially, option E does not mention an increase in global air pollution. That fact alone is not enough to reject E.

E shifts the focus to future cars. That move might be legitimate . . . if only the language were definitive.

Option E's language is not definitive at all. Not even a little bit.

Option E is a conditional statement signaled by the word "if." The language is speculative.

Option E discusses a POSSIBLE condition and a probable result. The modal verbs "could" and "should" are red flags that convey "nothing definite here!"

We have a statement that air pollution
-- COULD still increase . . .
-- IF total vehicle use . . .
-- SHOULD (hypothetically WERE TO) increase "significantly."

I read option E and thought, "Spineless. Wishy-washy. How do we know whether these big IFs will happen? We don't."

That language is too uncertain and cautious to do any harm, never mind to "seriously weaken" the conclusion. IF total vehicle use "should" (were to) increase significantly, pollution "could" also increase.

I sense that option E seems viable because people are failing to notice key words, often modifiers, in the conclusion.

I am glad to see your energy put into rewriting the conclusion. Smart move. Now the task includes noticing every word.

I often pick out nouns and adjectives first, between three and five.

In this case I would pick
-- old U.S. cars
-- pollution
-- decade
-- global atmosphere

Then I string my choices together (usually in my head, or scribbled quickly with symbols).

My paraphrased conclusion is: Old U.S. cars' pollution of the global atmosphere will decrease in the next decade.

In a CR or LR conclusion, words that may seem extra are not. Every word matters, especially modifiers of any kind such as adjectives.

The importance of the words "U.S." [cars] and "global" [atmosphere] in the conclusion has not been mentioned explicitly, but those two adjectives should jump out clearly now. They are the key to the finding the correct answer.
This focus led you the wrong way.

The logical link is not between new and old cars. The premises discuss new cars a lot. While premises are important, they also can distract if we do not watch for the modifiers that actually show up in the conclusion.

New cars are not mentioned in the conclusion. (When in doubt, go right back to the conclusion and look at the words.)

The crucial logical link is between "old U.S. cars" and "global pollution," both of which are mentioned in the very first sentence of the prompt and repeated in the conclusion.

This question is from the LSAT.
When I tutor for the LSAT (half of questions are Logical Reasoning, which are like CR on amphetamines), I give aspirants three basic start points, all of which apply to CR:

1) Accept that the author's facts are true, no matter how outrageous, stupid, or irrelevant you think they are. The facts are true. Do not embellish, alter, or argue with them.

2) But go to war with the author's conclusion. If you are short on time, read the conclusion more carefully than anything else. Get fierce and get personal: this conclusion is idiotic and the author is feeding you a load of hooey.

3) Tell the author WHY he or she is spewing nonsense.

Your first instinct should be to attack. (Even in strengthen questions, attack. If you attack, you will find the best supporting answer.)

Intellectual exercises in critical thinking often are supposed to be polite and measured. Not here. Abandon deference.

If we are in attack mode regarding the author's conclusion, we are less likely to be swayed by reasonable-sounding answers that do little or nothing to show that the conclusion is wrong and dumb.

What could we do in this case to explain to the author WHY we are not buying his or her nonsense?

I started by contradicting the conclusion. Old U.S. cars contribute disproportionately to global air pollution. Those cars' contribution to global pollution will NOT decrease if?

If somehow those old cars get back on the road and emit the same amount of pollution.

We therefore want an answer in which the old U.S. cars show up in some other place without emission controls -- in the next county or state or country.

That answer is C. Option (C) demolishes the conclusion.
Big markets exist for old U.S. cars. Those markets do not regulate pollution. Result? The old U.S. cars still drive around, polluting the global atmosphere disproportionately. Nothing changed!

"Dear author: if old U.S. cars simply move, pulled by demand in 'thriving markets' for those cars; and if old U.S. cars then operate in places without pollution controls; then the disproportionate contribution to global atmosphere pollution by old U.S. cars will not decrease. You are full of hooey. The end."

Answer C

Hope that helps.