单项选择题
A tug is towing three manned barges in line in fog. The first vessel of the tow should sound （）.
A.no fog signal B.one short blast C.one prolonged and three short blasts D.one prolonged，one short，and one prolonged blast
单项选择题 A triangular daymark would be colored（）.
单项选择题 A towing vessel 30 meters in length is pushing barges ahead. How many white masthead lights is the vessel REQUIRED to show at night?（）
单项选择题 A towing light，according to the Rules，is a（）.
