单项选择题
A.two all-round red lights in a vertical line
B.anchor lights and sidelights
C.two all-round white lights in a vertical line，sidelights and a stern light
D.two all-round red lights in a vertical line，sidelights，and a stern light
单项选择题 A vessel may use any sound or light signals to attract the attention of another vessel as long as（）.
单项选择题 A vessel may exhibit lights other than those prescribed by the Rules as long as the additional lights（）.
单项选择题 A vessel is underway with a work stage rigged over the side. A seaman may work on the stage，but only when（）.