The correct answer is A) two all-round red lights in a vertical line. According to the International Regulations for Preventing Collisions at Sea (COLREGS), a vessel not under command, underway but not making way, is required to exhibit two all-round red lights in a vertical line. This signals to other vessels that the ship is not under command and cannot maneuver as required. The other answer choices are incorrect because a stern light is only required for a vessel underway and making way, and sidelights are used to indicate the vessel's direction of travel, which a vessel not under command would not be able to control.