单项选择题
A.at anchor
B.mine-clearing
C.engaged in fishing
D.engaged in towing
单项选择题 A vessel fitted with twin screws is easier in（）than a vessel with single screw.
单项选择题 A twin-screw vessel is easier to maneuver than a single-screw vessel because the twin-screw vessel（）.
单项选择题 A twin-screw vessel can clear the inboard propeller and maneuver off a pier best by holding a(n)（）.