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Difficulty: EasyRecognizing Explicit Cause and Effect

In the semi-arid region of the Karst Plateau, geologists have long monitored the sudden collapse of surface soil, a phenomenon locally known as "swallow holes." While subterranean water flow is the primary long-term driver of this geological erosion, the immediate trigger for these sudden cave-ins is often human activity. Specifically, during the agricultural expansion of the 1970s, farmers installed extensive underground drainage pipes to redirect seasonal runoff away from their crops. This concentrated redirection of water significantly increased the local water pressure against the delicate limestone ceiling of the underground caverns. Consequently, the structural integrity of the limestone weakened rapidly, culminating in the widespread collapses observed today. Although some local residents attributed the cave-ins to recent seismic tremors, geological sensors recorded no significant tectonic activity during the major collapse events. Instead, the data confirmed that the redirecting of surface runoff was the direct catalyst for the structural failures.

According to the passage, the immediate trigger for the sudden collapse of surface soil in the Karst Plateau was which of the following events?

  1. the concentrated redirection of seasonal runoff through underground drainage pipesAnswer
  2. B
    the natural long-term erosion of the limestone ceiling by subterranean water flow
  3. C
    the pressure of collapsing surface soil forcing runoff into the underground caverns
  4. D
    recent seismic tremors and tectonic shifts occurring along the plateau

Answer

The concentrated redirection of seasonal runoff through underground drainage pipes
The passage explicitly states that the redirecting of surface runoff was the direct catalyst for the structural failures (collapses). This was achieved when farmers installed drainage pipes to redirect seasonal runoff away from crops.

Step-by-Step Solution

1
Identify the key effect in the question stem.
The effect is the sudden collapse of surface soil (swallow holes) in the Karst Plateau.
The question asks specifically for the immediate trigger (cause) of this collapse.
2
Locate the explicit cause in the text.
The text states that 'redirecting of surface runoff was the direct catalyst for the structural failures.'
We must find the sentence linking the collapses to their direct trigger.
3
Match the literal cause to the correct answer choice.
The option containing the redirection of seasonal runoff via drainage pipes matches this explicit statement.
This confirms the correct option based on literal comprehension of the text.

Key Concept

Recognizing Explicit Cause and Effect
Estimated Time:45s
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Topics

Recognizing Explicit Cause and Effect

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