What must be kept in mind when securing switches or derails where locking is not possible?

When securing switches or derails where locking is not possible, all aspects highlighted in the choices are crucial for ensuring safety and operational integrity.

First, the need for a supervisor check emphasizes the importance of oversight and accountability in train operations. A supervisor's evaluation helps to confirm that appropriate securing measures are taken, and it provides an additional layer of safety by having another qualified person verify the operation's readiness.

Maintaining proper communication is also vital in situations where locking is not possible. Effective communication among crew members ensures that all personnel are aware of the current state of the switches or derails and any precautions that need to be taken. This reduces the risk of miscommunication that could lead to accidents or operational errors.

Lastly, evaluating the conditions of the equipment is necessary to assess whether the switches or derails are functioning correctly and safely. Any deficiencies in equipment need to be identified and addressed to prevent potential failures in functionality that could lead to incidents.

Considering all these factors creates a comprehensive approach to safely managing switches and derails that cannot be locked, which is why the correct response includes all of these aspects.