What lights are shown by a pushing vessel and a vessel being pushed when connected in a composite unit?

When a pushing vessel and a vessel being pushed are connected in a composite unit, they are regarded collectively as a single power-driven vessel under the COLREGs. This means that they must display the lights required for a power-driven vessel, including a masthead light, sidelights, and a stern light.

The reason for displaying the lights of a power-driven vessel, rather than those of a sailing vessel or showing no lights, is to ensure that other vessels can easily identify the nature of the composite unit on the water. This identification is crucial for safe navigation and the prevention of collisions, as it informs other mariners about the size, maneuverability, and type of the unit. Therefore, the correct answer reflects the need for safety and clarity in maritime navigation by adhering to the requirements set out in the COLREGs for power-driven vessels.