单项选择题
Preferred channel marks are aids to navigation which all following marks other than（）．
A.channel junctions B.bifurcations C.fishing traps D.wrecks or obstructions
单项选择题 In the absence of a route leading from seaward，the conventional direction of buoyage generally follows（）.
单项选择题 In regions where ice conditions prevail in the winter，（）.
单项选择题 A vessel shall not（）.
