单项选择题
A vessel may use any sound or light signals to attract the attention of another vessel as long as（）.
A.white lights are not used
B.red and green lights are not used
C.the signal cannot be mistaken for a signal authorized by the Rules
D.the vessel signals such intentions over the radiotelephone
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（）.
单项选择题 A vessel is to make a voyage between New York and San Juan，Puerto Rico，and return. The crew should be signed on（）.