What must a conductor monitor along the route?

The correct choice highlights the crucial responsibilities of a conductor, particularly in relation to safety and operational effectiveness. Conductors are tasked with monitoring vital signs and signals along the route to ensure that the train operates within safe parameters. This includes keeping an eye on signals that indicate track conditions, upcoming stops, and any potential hazards.

Monitoring vital signs and signals is essential for maintaining safe train operations, allowing the conductor to respond swiftly to any irregularities or issues that may arise. This vigilance is a fundamental aspect of the conductor's role, which fundamentally revolves around ensuring the safety of both the train crew and passengers throughout the journey.

While monitoring weather patterns, managing food supplies, or understanding passenger preferences are important aspects of train operations, they do not directly relate to the core safety and operational monitoring responsibilities of the conductor, which is why they are not the primary focus of the conductor's duties.