A power-driven vessel towing another vessel astern (tow less than 200 meters) shall show which light(s)?

When a power-driven vessel is towing another vessel astern and the tow is less than 200 meters in length, the proper light configuration is to display two masthead lights in a vertical line. This arrangement helps distinguish the towing vessel from other types of vessels and indicates that it is engaged in towing operations. The additional masthead light signifies that there is a tow involved and gives other vessels clear information about the nature of the vessel's activities.

While the first option mentions showing one masthead light, this does not provide sufficient indication that the vessel is engaged in towing, particularly when the tow is significant in size. The sidelights are essential for all vessels, but they do not convey the specific towing status. A special flashing light is typically used in different scenarios, such as for vessels engaged in fishing or for vessels that are constrained by their draft, and does not apply in this towing situation. Therefore, the display of two masthead lights in a vertical line is the correct indication for power-driven vessels engaged in towing operations within the specified parameters of length.