During a pre-trip inspection, what is a sign that brake linings may be unsafe?

During a pre-trip inspection, observing brake linings worn to a dangerous thinness is a clear indication that they may be unsafe. Brake linings are crucial for effective braking, and their thickness directly impacts performance. When the linings are excessively worn, they can compromise the vehicle's ability to stop efficiently, leading to potential accidents and safety hazards.

While options related to a shiny, reflective surface, dust accumulation, or the absence of visible markings may indicate wear or other issues with brake linings, they are not as definitive as the thickness of the linings. A shiny surface can suggest overheating, but it does not necessarily correlate directly with insufficient braking capability. Dust accumulation is often normal due to brake use but doesn’t itself indicate that the linings are unsafe. Finally, the absence of markings may raise concerns about the linings but does not provide information on their safety or functionality. Therefore, the most reliable indicator of unsafe brake linings is their excessive wear.