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Difficulty: EasyOverall Text Structure Analysis

Dendrochronologists analyze the annual growth rings of ancient trees to reconstruct historical climate variations. In a recent study of subalpine conifers in the Sierra Nevada, researchers observed a series of unusually narrow and frost-damaged rings dating to the mid-sixth century CE. The researchers hypothesized that this stunted growth was caused by a major volcanic eruption that released sunlight-blocking sulfate aerosols into the atmosphere, leading to a decade of colder summers. To test this hypothesis, they compared their tree-ring data with ice core samples from Greenland, which revealed a corresponding spike in volcanic ash from the exact same period, thereby confirming the volcanic trigger.

Which choice best describes the overall structure of the text?

  1. A
    It details a historical debate, explains two contrasting methods of investigation, and argues that one method is superior.
  2. B
    It explains a common biological technique, identifies its main limitation, and proposes a solution to overcome it.
  3. It introduces a scientific observation, outlines a hypothesis proposed to explain it, and describes a comparison used to support that hypothesis.Answer
  4. D
    It presents a general ecological principle, describes how it was discovered, and lists its modern applications.

Answer

It introduces a scientific observation, outlines a hypothesis proposed to explain it, and describes a comparison used to support that hypothesis.
The correct answer is the option stating that the text introduces a scientific observation, outlines a hypothesis proposed to explain it, and describes a comparison used to support that hypothesis. The text starts with a specific observation (unusually narrow and frost-damaged tree rings), followed by a proposed explanation (a major volcanic eruption), and finishes by detailing a comparative test (using Greenland ice core samples) that supports this explanation.

Step-by-Step Solution

1
Analyze the first part of the text.
The text begins by explaining what dendrochronologists do and then describes a specific finding: unusually narrow and frost-damaged tree rings from the mid-sixth century CE. This represents a scientific observation.
To identify the initial rhetorical move of the passage.
2
Analyze the middle part of the text.
The researchers suggest that a major volcanic eruption caused this growth pattern by blocking sunlight and cooling the climate. This represents a proposed hypothesis to explain the observation.
To trace the development of the passage's explanation.
3
Analyze the final part of the text.
The researchers compare the tree-ring data with Greenland ice core data, finding volcanic ash that confirms their hypothesis. This describes a comparison used to validate the hypothesis.
To determine the concluding rhetorical move of the passage and match the overall sequence to the correct option.

Key Concept

Overall Text Structure Analysis
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Topics

Overall Text Structure Analysis

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