What type of vessel shall show no stern light but exhibit two yellow lights in a vertical line?

The correct answer indicates a specific type of vessel as defined by the International Regulations for Preventing Collisions at Sea (COLREGs). A power-driven vessel that is pushing ahead in the Great Lakes or similar situations shows two yellow lights in a vertical line to convey its operational status. This configuration is prescribed to help other vessels identify that the pushing vessel is one that is engaged in a specific activity, such as pushing a barge or another vessel ahead of it without the need for a stern light.

In this case, the absence of a stern light emphasizes that the vessel is not presenting itself as a standard power-driven craft but rather as one engaged in a particular maneuvering task, which is critical information for surrounding vessels. This lighting arrangement helps ensure safe navigation and allows for proper recognition and response from other vessels in the vicinity.

The other choices represent different scenarios or types of vessels, each governed by distinct lighting requirements according to the COLREGs. For instance, sailing vessels of less than 20 meters have their own specific lighting rules, and vessels engaged in fishing or under sail with machinery would follow different protocols.