What must crew members do immediately after passing a signal that displays a stop indication?

Answer: B — Warn other trains and stop the train immediately

When a crew member observes a signal displaying a stop indication, the appropriate and immediate response is to warn other trains and stop the train promptly. This action is critical for maintaining the safety of rail operations and ensuring that all crew members are aware of potential hazards ahead. The need to stop is based on the principle of preventing accidents and ensuring that the train does not proceed into a dangerous situation. By stopping, the crew can assess the situation ahead, communicate with dispatch, and receive instructions on how to proceed safely. Moreover, warning other trains is vital for ensuring the entire rail network is informed about the stop condition to prevent collisions. This response reflects an understanding of the importance of adhering to signals and the protocols put in place to guarantee the safe operation of trains on the network.