The proliferation of colloquialisms is degrading the English language. - This is the main conclusion by the author
A phrase such as she was like, "no way!" you know?—a meaningless collection of English words just a few decades ago—is commonly understood by most today to mean she was doubtful. - An example in line with the Main conclusion
No language can admit imprecise word usage on a large scale without a corresponding decrease in quality. - Claim made by the author to support the Main Conclusion
Now that the structure is clear, just focus on the GAP. The argument jumps from the Premise to the Claim and introduces the Conclusion with an unfamiliar word Colloquialism. Now, all we need is to bridge the GAP between imprecise word in large scale degrading language quality and Colloquialism degrading English language.
Bunuel
The proliferation of colloquialisms is degrading the English language. A phrase such as she was like, "no way!" you know?—a meaningless collection of English words just a few decades ago—is commonly understood by most today to mean she was doubtful. No language can admit imprecise word usage on a large scale without a corresponding decrease in quality.
The argument relies on which of the following assumptions?
(A) Colloquialisms always evolve out of a meaningless collection of words.
(B) The colloquialisms appearing in the English language introduce imprecision into the language on what would be considered a large scale.
(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.
(D) The English language would not be degraded if there did not exist an alternative informal way to express the sentiment "she was doubtful."
(E) The widespread use of colloquialisms represents the most serious form of language degradation.
(A) Colloquialisms always evolve out of a meaningless collection of words.
This is too extreme. Even if we negate this choice i.e. "C NOT always evolve out of a meaningless collection of words.", meaning, sometimes it evolves from a meaningless collection, right? Therefore, the negation won't actually break the conclusion.
(B) The colloquialisms appearing in the English language introduce imprecision into the language on what would be considered a large scale. This what we need. If it would NOT have been considered large scale, then there is no need to conclude that Collo. is degrading the English language. [refer to 3rd sentence in the passage.]
(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.
Other languages are none of our concern.
(D) The English language would not be degraded if there did not exist an alternative informal way to express the sentiment "she was doubtful."
Can you see that this choice completely focuses on a point which was presented as a mere example in the argument as Main Point for the assumption. [Typical Gmat traps in hard level questions, option makes judgement by making a point as a main point of the argument which the Author never expressed as Main Point]. In other words, it is not a Must Be True scenario.
(E) The widespread use of colloquialisms represents the most serious form of language degradation.
The seriousness of the cause is none of our concern. The fact that it is still a cause makes this option irrelevant.Hope it helps,
Thanks :)