单项选择题
A single towing light will be carried above a vessel’s sternlight（）.
A.only if she is towing astern B.only if the tow exceeds 200 meters C.at any time when towing D.if the towing vessel is part of a composite unit
单项选择题 A safe water daymark has what shape? （）
单项选择题 A red triangular daymark marks（）.
单项选择题 A power-driven vessel，when towing astern，shall show（）.
