单项选择题
A tug may be in danger of tripping when（）.
A.towed sideways by an overwhelming force on the towline B.her tow moves parallel to and forward on either side of the tug C.the tow is no longer directly astern but moves up on her quarter D.All of the above
单项选择题 A tug is best positioned for towing and maneuvering on rivers and other restricted waters where wave action is limited when（）.
单项选择题 A tug is “in irons” when held in a fixed position by（）
单项选择题 A tug in irons is（）.
