单项选择题
A towing vessel pushing a barge ahead and rigidly connected in a composite unit shall show the lights of（）.
A.a vessel towing by pushing ahead B.a power-driven vessel，not towing C.a barge being pushed ahead D.either answer A or answer B
单项选择题 A towboat is pushing barges ahead at a dangerously fast speed when（）.
单项选择题 A tow of 9 barges is made up three abreast and three long. The towboat is faced up to the center string which is known as the（）.
单项选择题 A spreader bar is used to（）.
