Which of the following conditions requires a crew member to provide protection against possible movement of a standing train?

Providing protection against the possible movement of a standing train is crucial to ensure the safety of crew members and any workers in the vicinity. When a train is standing within the limits while switching, the risk of unintended movement increases due to various factors, such as a miscommunication or mechanical issues. Therefore, under these conditions, crew members are required to take additional safety measures, such as setting proper warnings or deploying safety equipment to alert others and prevent accidents.

In contrast, situations like moving at maximum speed, stopping at a signal, or waiting for a signal change do not inherently require the same level of protective measures against train movement, as these activities are typically governed by established operating protocols that ensure safety while the train is in motion or at a stop for signals. The focus in those scenarios is more on adhering to signals and regulations rather than actively protecting against the potential movement of a vehicle that is already stationary.