Which of the following circuit breakers could affect door operation in an M-3 car?

The door operator circuit breaker is crucial for the functionality of the doors in an M-3 car. This breaker specifically manages the electrical system that controls the opening and closing mechanisms of the doors. If this circuit breaker trips or fails, it would directly interrupt the power supply to the door operator, preventing the doors from functioning properly. Ensuring this circuit breaker is operational is essential for the safe boarding and alighting of passengers, making it a key component in the overall safety and efficiency of train operations.

Other circuit breakers listed, while important for different operations of the train, do not directly influence the door mechanisms. The air compressor circuit breaker relates to the pneumatic systems used for braking and other functions, the engine control circuit breaker is tied to the locomotive's engine management, and the signal light circuit breaker governs the illumination for signals but not door operation. Thus, only the door operator circuit breaker has a direct impact on whether the doors can open and close, highlighting its critical role in the M-3 car's operation.