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Difficulty: MediumContrast and Reversal Clues

Although early observational models postulated that interstellar dust grains within dense molecular clouds were entirely ________, devoid of internal chemical reactivity, recent high-resolution spectroscopic analyses reveal complex ice mantles actively catalyzing organic synthesis.

Which of the following words best completes the sentence?

  1. inertAnswer
  2. B
    dynamic
  3. C
    volatile
  4. D
    pervasive
  5. E
    intricate

Answer

inert
The word 'inert' means chemically inactive or unreactive. The sentence structure hinges on the reversal signal 'Although', contrasting early beliefs with recent evidence that interstellar dust grains actively catalyze chemical reactions. The modifying phrase 'devoid of internal chemical reactivity' confirms that 'inert' is the exact word required.

Step-by-Step Solution

1
Identify structural transition signals.
The opening word 'Although' establishes a contrast between early observational models and recent spectroscopic discoveries.
Contrast signals require the missing word in the initial clause to express the semantic opposite of the findings presented in the subsequent clause.
2
Analyze local contextual definitions and targets.
The blank is directly explained by the appositive phrase 'devoid of internal chemical reactivity' and stands in opposition to 'actively catalyzing'.
The target word must precisely convey chemical passivity or inactivity.
3
Evaluate answer choices to select the precise contextual fit.
'Inert' specifically denotes chemical inactivity, satisfying both the local structural clue and the macro contrast.
Among the choices, only 'inert' correctly matches the required meaning of lacking activity.

Key Concept

Using contrast signals (e.g., 'although') to identify opposite semantic relationships across sentence clauses.
Estimated Time:1m 0s
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Topics

Contrast and Reversal Clues

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