What does the presence of two masthead lights on a towing vessel indicate?

Answer: C — It is less than 50 meters long with a tow less than 200 meters

The presence of two masthead lights on a towing vessel indicates that the vessel is less than 50 meters in length and is towing another vessel. According to the COLREGs, a towing vessel that is under 50 meters long must exhibit two masthead lights to communicate its position and operational status clearly. This configuration assists other vessels in recognizing the size and nature of the towing situation, ensuring safe navigation in close quarters. Options that suggest the vessel is over 50 meters long or solely under sail are not relevant to the situation described, as the specific requirement for the two masthead lights applies to those towing vessels that fall under the stated length criteria. Additionally, a vessel towing another vessel would require the display of certain lights, including the two masthead lights, to signal its operation effectively to nearby vessels.