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Difficulty: MediumExplicit Main Idea

High-pressure turbine blades in modern jet engines operate in environments that exceed the melting point of their underlying metal alloys. To survive these extreme conditions, advanced ceramic thermal barrier coatings are applied directly to turbine surfaces to insulate the base metal from destructive exhaust heat. These multi-layer ceramic coatings can lower the substrate alloy's surface temperature by up to 300 degrees Fahrenheit. While specialized internal cooling channels also circulate compressed air through the blade core, the ceramic barrier remains the primary defense against thermal degradation. Without this insulating ceramic layer, turbine components would rapidly suffer structural failure and creep deformation.

Which of the following statements best expresses the main idea of the passage?

  1. A
    Specialized internal cooling channels circulate compressed air through the blade core to lower internal temperatures.
  2. B
    Modern jet engines require all structural components to be constructed from multi-layer ceramic materials.
  3. Ceramic thermal barrier coatings are applied to protect jet engine turbine blades from damaging operational heat.Answer
  4. D
    Ceramic coatings reduce the surface temperature of underlying turbine alloys by up to 300 degrees Fahrenheit.

Answer

Ceramic thermal barrier coatings are applied to protect jet engine turbine blades from damaging operational heat.
The passage explicitly states that ceramic thermal barrier coatings are applied directly to turbine surfaces to insulate the base metal from destructive heat, which constitutes the central claim and focus of the entire paragraph.

Step-by-Step Solution

1
Read the passage and locate the explicit topic sentence that anchors the entire discussion.
The second sentence explicitly states that ceramic thermal barrier coatings are applied directly to turbine surfaces to insulate the base metal from destructive heat.
Explicit main idea questions require identifying the direct statement of the author's central claim.
2
Evaluate the surrounding sentences to verify if they serve as supporting details for this central claim.
The subsequent sentences provide supporting evidence, such as the specific temperature reduction and the role of internal cooling channels.
Distinguishing between the central claim and supporting evidence ensures the chosen statement represents the entire paragraph.
3
Match the core claim to the option that accurately paraphrases it without altering scope.
The statement expressing that ceramic thermal barrier coatings are applied to protect jet engine turbine blades from damaging operational heat directly matches the topic sentence.
The correct answer must represent the primary message rather than a secondary detail or overextension.

Key Concept

Identifying explicitly stated topic sentences that state the central purpose and claim of a paragraph.
Estimated Time:1m 0s
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Explicit Main Idea

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