What characterizes a liner in maritime shipping?

A liner in maritime shipping is characterized by operating on a regular schedule with predetermined routes and consistent ports of call. This means that a liner service is designed to provide reliability and predictability, often catering to both cargo and passenger transportation needs. The scheduled nature allows shippers to plan logistics effectively, knowing when to expect vessels at different ports.

Unlike irregular operators that may change their routes or schedules based on demand or other factors, liners adhere to fixed itineraries. This predictability is crucial for businesses that rely on timely deliveries and shipping schedules. Liners often carry a mix of cargo types, but the emphasis is on maintaining a structured service, which is why option B accurately defines their operation.

The other options describe characteristics that do not align with the definition of a liner, such as operating irregularly or specializing exclusively in certain types of cargo or passenger services.