单项选择题
A tug is “in irons” when held in a fixed position by（）
A.the weight of its tow，its being anchored，or grounded B.the weight of its towing hawser on the bottom C.an adverse current D.lack of power or an engine breakdown
单项选择题 A tug in irons is（）.
单项选择题 A tsunami is caused by a(n)（）.
单项选择题 A traffic separation zone is that part of a traffic separation scheme which（）.
