单项选择题
A.one blast，4 to 6 seconds in duration
B.three blasts，4 to 6 seconds in duration
C.one continuous blast until you are able to see around the bend
D.one blast，8 to 10 seconds in duration
单项选择题 You are under sail and overtaking a tug and tow.Which action is correct（）.
单项选择题 You are on a vessel that cannot comply with the spacing requirement for masthead lights.What is required in this situation（）.
单项选择题 You are Master of a towing vessel engaged in towing three barges astern.The middle barge of the tow would be required to sound which of the following during restricted visibility （）.