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Difficulty: HardImplicit Main Idea

Early submarine designers prioritized hydrodynamic hull contours to maximize submerged speed, yet acoustic sensors easily detected vessels even at modest throttle. Engineers then coated external bulkheads with elastomeric tiles to absorb outgoing engine vibrations, but internal mechanical hums continued to register on hydrophones. Subsequent overhauls isolated propulsion machinery on suspended rubber mounts and redesigned drive shafts with flexible couplings. Only after technicians simultaneously addressed hull resonance, structural mounting, and hydrodynamic turbulence did acoustic detection ranges decline significantly.

The passage as a whole primarily suggests that:

  1. A
    Modern naval vessels cannot achieve operational success without completely silent propulsion systems.
  2. B
    Elastomeric hull tiles are ineffective at dampening vibrations produced by internal machinery.
  3. Effective acoustic suppression in submarines depends on integrating multiple concurrent engineering solutions.Answer
  4. D
    Hydrodynamic hull design is obsolete because modern sonar systems render speed useless.

Answer

Effective acoustic suppression in submarines depends on integrating multiple concurrent engineering solutions.
The correct option captures the implicit synthesis of the entire text: individual engineering efforts provided only partial remedies, and meaningful acoustic reduction occurred only when hull dampening, mechanical isolation, and hydrodynamic shaping were integrated together.

Step-by-Step Solution

1
Analyze the sequential progression of details across the passage.
The narrative outlines successive engineering modifications (streamlined hulls, acoustic tiles, and suspended machinery mounts) that each failed to eliminate detection when implemented in isolation.
Understanding the limitation of each individual attempt reveals why no single sentence contains the complete main idea.
2
Evaluate the resolving condition described in the concluding sentence.
Acoustic detection ranges dropped significantly only after technicians combined solutions across hull resonance, structural isolation, and fluid dynamics at the same time.
The shift from failed single-system efforts to success through combined methods highlights the underlying thesis.
3
Synthesize the overarching unstated claim.
The author implicitly asserts that comprehensive stealth requires a multi-faceted, integrated engineering strategy rather than piecemeal fixes.
Synthesizing the collective evidence avoids selecting isolated facts or unjustified assumptions.

Key Concept

Synthesizing an implicit main idea from cumulative evidence
Estimated Time:1m 30s
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Topics

Implicit Main Idea

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