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Difficulty: EasyCausal Detail Extraction

Read the following passage:

Continuous welded rail (CWR) tracks expand significantly when exposed to sustained high summer temperatures. Because the steel rails are anchored tightly to concrete ties and cannot expand lengthwise, immense internal compressive stress builds up within the metal. If track maintenance crews fail to install adequate ballast shoulder support along the rail bed, this trapped thermal stress causes the tracks to buckle laterally, creating a hazardous alignment defect known as a sun kink. Consequently, dispatchers must impose speed restrictions during heatwaves to reduce dynamic train loads on vulnerable track sections.

According to the passage, what directly causes continuous welded rail tracks to buckle laterally during high summer temperatures?

  1. A
    The implementation of speed restrictions by train dispatchers during heatwaves
  2. The accumulation of internal compressive stress in rails prevented from expanding lengthwiseAnswer
  3. C
    Excessive dynamic train loads that generate sustained high ambient temperatures
  4. D
    Electrical current fluctuations occurring in overhead locomotive power lines

Answer

The accumulation of internal compressive stress in rails prevented from expanding lengthwise
The correct answer accurately reflects the direct causal statement in the text: because the steel rails cannot expand lengthwise when heated, internal compressive stress builds up and causes the tracks to buckle laterally.

Step-by-Step Solution

1
Locate the stated effect in the passage.
Identified the phrase 'causes the tracks to buckle laterally' in the third sentence.
The question asks specifically for the cause behind lateral track buckling.
2
Extract the explicit cause linked directly to this outcome.
Found that trapped thermal stress—created because heated steel rails cannot expand lengthwise—causes the buckling.
Causal detail extraction requires matching the stated cause to the target effect without distortion.

Key Concept

Causal Detail Extraction
Estimated Time:45s
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Topics

Causal Detail Extraction

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