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Difficulty: MediumImplicit Main Idea

During seasonal migration, geese and pelicans organize into distinct aerodynamic V-formations. As a bird flaps its wings, it creates circular vortices of air trailing from its wingtips, generating a zone of downward airflow directly behind its body and an upward stream of air along the outer edges of its wake. Subsequent birds position their wingtips precisely within this rising column of air, capturing lift without expending extra muscular effort. Heart rate telemetry reveals that trailing individuals exhibit significantly lower cardiac exertion and reduced wing-beat frequencies compared to the flock leader.

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

  1. A
    All avian flight behaviors have evolved primarily to maximize collective group survival during long-distance journeys.
  2. B
    Trailing birds maintain lower cardiac exertion and reduced wing-beat frequencies than the leader.
  3. V-formation flight enables migrating birds to conserve physical energy by utilizing the aerodynamic lift created by flock mates.Answer
  4. D
    Flock leaders possess greater endurance than other birds because they remain at the front for the entire migration route.

Answer

V-formation flight enables migrating birds to conserve physical energy by utilizing the aerodynamic lift created by flock mates.
The correct answer brings together both key components of the passage: the physical mechanism of capturing rising air vortices from preceding birds and the physiological benefit of decreased energy exertion. Because no single sentence in the paragraph states this complete conclusion, this synthesis represents the implicit main idea.

Step-by-Step Solution

1
Analyze the passage structure and identify the core subject and supporting facts.
The text discusses how birds flying in V-formations position themselves in trailing wingtip upwash to gain lift with less effort, corroborated by lower heart rates.
Understanding individual factual elements is necessary to identify how they collectively point to an unstated point.
2
Determine the underlying relationship connecting the physical airflow details to the physiological measurements.
The aerodynamic wake effect directly causes the physiological energy savings experienced by trailing birds.
An implicit main idea requires synthesizing cause-and-effect relationships across the whole text.
3
Formulate a comprehensive summary statement that encompasses the entire paragraph without introducing outside claims or narrowing to a single fact.
The overall point is that the V-formation serves as an energy-saving aerodynamic strategy during migration.
The correct choice must capture the unstated thesis without being overly broad, overly narrow, or unsupported.

Key Concept

Identifying an unstated main idea by synthesizing aerodynamic and physiological supporting details
Estimated Time:1m 0s
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Topics

Implicit Main Idea

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