Premise : No language can admit imprecise word usage on a large scale without a corresponding decrease in quality.
i.e. Using imprecise word on a large scale in any language results in decrease in quality.
Conclusion : The proliferation of colloquialisms is degrading the English language.

Prethink :
The conclusion does not stand until we believe (assume) these things :
How does colloquialism degrade the language? By decreasing the quality.
Decreasing the quality is correlated to the degradation of the language.
What is colloquialism? Using imprecise word on a large scale in any language
Using imprecise word on a large scale is colloquialism.

Let's look at the choices.
(A) Colloquialisms always evolve out of a meaningless collection of words.
This may or may not be true,however this information does not say anything about how colloquialisms is degrading the English language (until we explicitly state that "the meaningless words" actually degrade the quality).
(B) The colloquialisms appearing in the English language introduce imprecision into the language on what would be considered a large scale.
Correct. Using imprecise word on a large scale in any language is what the colloquialism called.
(C) The Russian, French, and German languages cannot admit imprecise word usage on a large scale without an inevitable decrease in the quality of those languages.
No such inference can be made about Russian, French and German.
(D) The English language would not be degraded if there did not exist an alternative informal way to express the sentiment "she was doubtful."
Colloquialism degrades the English language. However, expressing doubt by imprecise words is just an example. We have many examples. Just the absence of one example would not have changed anything about colloquialism .
(E) The widespread use of colloquialisms represents the most serious form of language degradation.
Two problems with this choice. There is no linear correlation implied between the extent of using colloquialisms and language degradation. The all that we know that they are correlated.
Also, colloquialisms result into language degradation. Colloquialism itself does not represent language degradation.

B

Conclusion: The proliferation of colloquialisms is degrading the English language.
Given: No language can admit imprecise word usage on a large scale without a corresponding decrease in quality.
Assumptions:
1. Must be the case of "imprecise word usage on a large scale" - that's why the author has concluded "colloquialisms is degrading the English language"

The argument relies on which of the following assumptions?

(A) Colloquialisms always evolve out of a meaningless collection of words.
- Irrelevant

(B) The colloquialisms appearing in the English language introduce imprecision into the language on what would be [b]considered a large scale.
[/b]-Correct

(C) The Russian, French, and German languages cannot admit imprecise word usage on a large scale without an inevitable decrease in the quality of those languages.
- Irrelevant

(D) The English language would not be degraded if there did not exist an alternative informal way to express the sentiment "she was doubtful."
- Too specific

(E) The widespread use of colloquialisms represents the most serious form of language degradation.
- Words "most serious" making it incorrect

Prethinking: The proliferation of colloquialisms can introduce so many words in a language without decreasing the quality.

The argument relies on which of the following assumptions?

(A) Colloquialisms always evolve out of a meaningless collection of words. -> Incorrect. We don't know for sure.

(B) The colloquialisms appearing in the English language introduce imprecision into the language on what would be considered a large scale. -> Yes, colloquialisms introduce so many words. Let's keep it.

(C) The Russian, French, and German languages cannot admit imprecise word usage on a large scale without an inevitable decrease in the quality of those languages. -> why we are something opposite, what author is proposing.

(D) The English language would not be degraded if there did not exist an alternative informal way to express the sentiment "she was doubtful." -> Incorrect.

(E) The widespread use of colloquialisms represents the most serious form of language degradation. -> Incorrect.

So, I think B.

KAPLAN OFFICIAL EXPLANATION:

How's that for eloquence? The strange part is that most of us really have no problem understanding the meaning of this phrase. Which is, in fact, the author's beef in the stimulus. He gets right to the point: the conclusion that the increase in colloquialisms degrades the English language. For evidence, the author then (1) gives us an example of a colloquialism, the illustrious phrase in the title above, and (2) states that imprecise word usage on a large scale basically decreases the quality of the language, hence, the tie in with the conclusion in the first sentence. The assumption resides in the gaps between these pieces of information; we were never told that these colloquialisms were rampant or imprecise. Indeed, the author states that imprecise words admitted on a large scale decrease a language's quality, without showing that colloquialisms really fall into either category. That omission constitutes the shift in scope. For the author's conclusion to be valid based on this evidence, he must assume that the evidence is relevant to the conclusion, and that colloquialisms are both imprecise and prevalent in English. The right answer choice, (B), picks up on both. Without this, the evidence simply doesn't lead all the way to the conclusion.

(A) focuses on the source of colloquialisms, which the author addresses but which plays a central role in neither the evidence nor the conclusion. This could or could not be true without impacting the conclusion.

(C) basically restates the evidence. If "no language" can permit such laxity, then these three languages would logically follow along, but since the stimulus already tells us this much, (C) is not a necessary assumption here.

An 800 test taker recognizes the difference between a stated piece of evidence and an unstated—yet required—part of an argument (i.e., its assumption).

(D), if anything, presents us with a flawed inference, which would only be accurate if the author assumed that the stated colloquialism were the only colloquialism in English, and that only colloquialisms degrade the English language. He assumes neither, so if this were an Inference question, (D) would be wrong on these counts. As far as being assumed—that is, being something that's required by the argument—(D) is even further off base.

(E) is too extreme. The author identifies one cause (proliferating colloquialisms) which leads to one effect (like, um, degraded English). To make this argument, he does not need to assume that this cause is more or less serious than any other. Even if colloquialisms were a minor part of this problem, the author's conclusion could still be valid.
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C would be a correct must be true inference: a subtle trap laid by Kaplan to make sure you are focusing on the correct goal.

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