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Difficulty: MediumDistinguishing Main Idea from Details

Hydraulic braking systems in modern motor vehicles depend on glycol-ether fluid to transfer pedal force directly to the wheel calipers. Over time, however, brake fluid naturally absorbs moisture from the atmosphere through microscopic pores in flexible rubber hoses and reservoir seals. As moisture content increases, the fluid's boiling point drops significantly from its dry rating. Under prolonged or heavy braking, friction generates extreme heat that can boil water-contaminated fluid, creating pockets of compressible vapor inside the brake lines. Because gas compresses while liquid does not, this vapor formation causes a soft pedal feel and severe loss of stopping power. Consequently, routinely inspecting and replacing brake fluid is critical to prevent moisture-induced hydraulic failure.

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

  1. A
    Moisture enters hydraulic brake systems through microscopic pores in rubber hoses and reservoir seals.
  2. Regularly servicing brake fluid is essential to maintain safe vehicle stopping power by preventing moisture-related hydraulic failure.Answer
  3. C
    Compressible steam bubbles in contaminated brake lines cause a spongy pedal and reduced braking pressure.
  4. D
    All modern vehicle hydraulic systems must eliminate liquid fluids to prevent vapor compression under high heat.

Answer

Regularly servicing brake fluid is essential to maintain safe vehicle stopping power by preventing moisture-related hydraulic failure.
The correct response synthesizes the complete argument of the passage: it connects the cause (atmospheric moisture absorption), the hazard (boiling and loss of braking pressure), and the essential conclusion (routine fluid maintenance is required for safe operation).

Step-by-Step Solution

1
Analyze the passage structure to identify the relationship between the supporting points and the final conclusion.
The text explains how atmospheric water enters brake lines, why this lowers the boiling point, and how boiling produces compressible gas that degrades braking performance, leading to the concluding necessity of regular replacement.
Distinguishing supporting technical mechanisms from the concluding takeaway reveals the author's primary purpose.
2
Evaluate the answer choices to differentiate isolated factual details from the overarching thesis.
Options mentioning microscopic hose pores or spongy pedal feel describe individual cause-and-effect links in the middle of the passage, while the statement emphasizing routine fluid replacement to maintain braking safety synthesizes the full scope of the text.
The main idea must encompass the entire passage rather than focus on a single piece of evidence or a narrow sub-point.

Key Concept

Distinguishing the central thesis from supporting factual details in technical expository text
Estimated Time:1m 0s
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Distinguishing Main Idea from Details

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