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Difficulty: HardTransitions: Contrast and Concession

In 1990, oceanographer John Martin proposed the 'iron hypothesis,' suggesting that fertilizing iron-deficient areas of the ocean with iron dust would stimulate massive phytoplankton blooms and significantly reduce atmospheric carbon dioxide. ________, subsequent marine experiments have revealed a major complication: while the iron additions do trigger rapid phytoplankton growth, very little of the captured carbon actually sinks to the deep ocean floor, as most of it is rapidly recycled within the surface waters.

Which choice completes the text with the most logical transition?

  1. A
    Furthermore
  2. B
    Consequently
  3. NonethelessAnswer
  4. D
    For instance

Answer

Nonetheless
The transition 'Nonetheless' is correct because it establishes a contrast or concession relation between the two sentences. The first sentence presents the optimistic theory that iron fertilization can significantly reduce atmospheric carbon dioxide. The second sentence introduces empirical evidence that complicates this claim by showing that the captured carbon is recycled in surface waters instead of sinking. This represents an unexpected limitation, making a concession transition appropriate.

Step-by-Step Solution

1
Analyze the relationship between the first and second sentences.
The first sentence describes John Martin's optimistic hypothesis that iron fertilization would reduce atmospheric carbon dioxide. The second sentence describes subsequent experiments showing a major limitation: the carbon does not actually sink to the deep ocean.
Understanding the logical flow is necessary to identify the correct transition category.
2
Determine the required transition type.
Since the second sentence introduces unexpected counter-evidence or a limitation that qualifies the first sentence, a contrast or concession transition is needed.
Matching the semantic relationship to the appropriate transition type narrows down the choices.
3
Evaluate the choices to find the contrast/concession transition.
The word 'Nonetheless' is a concession transition that fits the context of introducing an unexpected complication. The other options ('Furthermore', 'Consequently', 'For instance') represent addition, cause-and-effect, and exemplification, respectively.
Selecting the option that correctly signals concession completes the text logically.

Key Concept

Identifying transitions that signal contrast or concession between sentences.
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Topics

Transitions: Contrast and Concession

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