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Difficulty: HardImplicit Main Idea

During the rapid deployment of early field telegraph networks across arid territories, communication units repeatedly experienced severe signal attenuation despite unbroken copper wiring and fully charged batteries. Infrequent desert downpours caused porous untreated timber posts to draw moisture and alkaline mineral salts upward from the ground. This capillary absorption transformed the structural uprights into unintended electrical conduits, draining current directly into the earth at hundreds of intermediate contact points. Maintenance crews initially attempted to resolve the failures by boosting transmission voltage, which accelerated line overheating and power depletion. Reliable message transmission was restored only after crews installed resin-coated brackets to isolate the wiring from the conductive wooden supports.

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

  1. A
    Technological infrastructure inevitably experiences system-wide failures when deployed in desert environments without specialized mechanical upgrades.
  2. B
    Alkaline mineral salts absorbed from desert soil transform damp wooden support posts into active electrical conduits during rainfall.
  3. Resolving the field communication breakdowns required insulating line supports against ground leakage rather than increasing electrical transmission power.Answer
  4. D
    Early telegraph line maintenance crews lacked the technical knowledge necessary to operate and maintain high-voltage battery equipment in the field.

Answer

Resolving the field communication breakdowns required insulating line supports against ground leakage rather than increasing electrical transmission power.
The correct response accurately synthesizes the unstated central message: the passage describes an unexpected grounding issue caused by damp, mineralized posts, shows that simply raising transmission voltage was ineffective, and demonstrates that physical insulation was the true remedy. Connecting these elements produces the implied central idea.

Step-by-Step Solution

1
Identify the primary problem and the initial failed intervention described in the passage.
The telegraph lines experienced severe signal loss due to current draining through wet, salt-laden wooden posts, and boosting transmission voltage failed to fix the issue.
Understanding the conflict and why the initial brute-force approach failed is necessary to identify what the author is highlighting.
2
Identify the ultimate resolution that restored operational capability.
Installing resin-coated brackets physically isolated the copper wiring from the posts, successfully stopping electrical leakage into the ground.
The contrast between the failed method (increasing power) and the working solution (insulating the supports) reveals the author's underlying point.
3
Synthesize the problem, the failed attempt, and the final solution into a single overarching thesis.
The core message is that overcoming these network failures required targeted structural insulation against grounding rather than merely increasing electrical power.
An implicit main idea must encompass the entire scope of the passage without narrowing down to individual details or making unsupported broad claims.

Key Concept

Synthesizing an implicit main idea by identifying the relationship between a central problem, a failed remedy, and the ultimate corrective action.
Estimated Time:2m 0s
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Implicit Main Idea

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