单项选择题
A.shown at the bow
B.white in color
C.shown in addition to the stern light
D.an all-round light
单项选择题 A towing hook may be released from the（）.
单项选择题 A tow that is properly aligned to pass through a narrow opening between two bridge piers is “ （）”.
单项选择题 A tow of 9 barges is made up three abreast by three long. The towboat is faced up to the last barge of the center string. The outer two strings of barges are the（）.