What duration is assigned to a holding test for a train that is 500 meters long?

The assigned duration for a holding test for a train that is 500 meters long is determined by established guidelines for train movements and safety procedures. For a train of this length, the correct duration is typically set at 25 minutes. This duration allows adequate time for operational checks, ensuring all systems function correctly while minimizing disruption to the rail network.

In the context of train operations, a holding test is crucial for safety, as it ensures that all safety protocols are followed and equipment is functioning properly before a train is allowed to proceed. The choice of 25 minutes reflects a balance between thorough testing and the necessity to keep train schedules on track.

The other choices reflect longer durations that exceed the standard expected for a train of this length, which could potentially affect scheduling and efficiency within the rail system. Therefore, the correct answer clearly stands out as aligning with operational standards for a train of this size.