单项选择题
A vessel engaged in（）shall not impede the passage of any other vessel navigating within anarrow channel or fairway.
A.mine clearance operation B.towing operation C.dredging or surveying or underwater operation D.fishing
单项选择题 A vessel aground would show the same dayshape as a（）.
单项选择题 A survey (special purpose mark) buoy（）.
单项选择题 A gas-free certificate would usually be issued by a(n)（）.
