What equipment is crucial for receiving and displaying cab signals on a train?

Answer: B — Train Control Apparatus

The Train Control Apparatus is essential for receiving and displaying cab signals on a train because it is specifically designed to process the information received from the track and convey important operational data to the crew. This system enhances safety by providing real-time information about the train's speed, track conditions, and upcoming signals directly in the locomotive's cab. In the context of train operation, cab signals are critical for maintaining safe speeds and preventing collisions, especially in areas with complex signaling systems. The Train Control Apparatus ensures that the crew has access to this vital information instantly, allowing for informed decision-making while operating the train. The other equipment options have differing roles. The automatic brake system is primarily focused on slowing and stopping the train safely but does not handle signal information. The passenger information system provides updates and notifications for passengers but is not involved in the cab signal process. Meanwhile, the engine diagnostics unit monitors the locomotive's performance and condition but is unrelated to signal reception or display. Thus, the Train Control Apparatus is the key system for managing cab signals effectively.