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Difficulty: MediumInferring Author Purpose and Intent

Submarine commanders navigating deep ocean waters must constantly monitor thermoclines—distinct horizontal layers where water temperature drops sharply with depth. Because the speed of sound is directly governed by water temperature and pressure, acoustic sonar pulses bend away from warmer layers and refract across these thermal boundaries. This physical phenomenon creates acoustic shadow zones where vessels can conceal their acoustic signatures from surface detection. By understanding how thermal gradients manipulate sonar propagation, naval operators can strategically position their vessels beneath thermocline layers to evade active surface pinging while maintaining surveillance of nearby maritime traffic.

Which of the following best describes the author's primary purpose in the passage?

  1. A
    Define thermoclines as distinct horizontal layers where water temperature drops sharply with depth
  2. Explain how underwater thermal layers influence sonar propagation and vessel concealmentAnswer
  3. C
    Argue that active surface sonar has become obsolete in modern naval warfare
  4. D
    Provide step-by-step technical instructions for calibrating sonar frequencies at sea

Answer

Explain how underwater thermal layers influence sonar propagation and vessel concealment
The author explains the scientific principle of how temperature layers refract sound waves and connects this mechanism directly to how naval operators exploit these layers to conceal submarines. This synthesis reflects the complete scope and primary communicative purpose of the passage.

Step-by-Step Solution

1
Analyze the passage structure and central topic
The text discusses thermoclines, how they alter sound wave paths (sonar propagation), and how submarines use this phenomenon to hide from surface sonar.
Determining what the passage covers as a whole is necessary to infer why the author wrote it.
2
Differentiate between supporting details and the author's overarching purpose
The definition of thermoclines in the opening sentence is background context supporting the larger explanation of acoustic shadow zones and tactical concealment.
A passage's primary intent encompasses the full scope of ideas rather than isolated introductory facts.
3
Evaluate the rhetorical tone and goal of the author
The tone is explanatory and informative, describing a physical principle and its practical tactical outcome.
Identifying the rhetorical mode ensures the selected answer reflects an explanatory goal rather than an argumentative or procedural one.

Key Concept

Inferring Author Purpose and Intent
Estimated Time:1m 0s
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Inferring Author Purpose and Intent

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