单项选择题
A power-driven vessel，when towing astern，shall show（）.
A.two towing lights in a vertical line B.a towing light in a vertical line above the sternlight C.two towing lights in addition to the sternlight D.a small white light in lieu of the sternlight
单项选择题 A power-driven vessel underway shall keep out of the way of（）.
单项选择题 A power-driven vessel towing another vessel astern (tow less than 200 meters) shall show （）.
单项选择题 A power-driven vessel shall have her engine ready for（）when the visibility is restricted.
