单项选择题
A 200-meter vessel is aground in fog. Which signal is optional? （）
A.A bell signal B.A gong signal C.A whistle signal D.All of the above
单项选择题 A vessel will NOT show sidelights when（）.
单项选择题 Two short blasts of the whistle have all of the following meanings EXCEPT（）.
单项选择题 Which vessel，when anchored at night，is NOT required to show anchor lights?（）.
