单项选择题
A.the centerline of a navigable channel B.the starboard side of a channel C.a prominent object of navigational interest that has no lateral significance D.an area of a channel where passing another vessel is permitted
A.heavy rain within six hours B.a decrease in wind velocity C.a change in the present weather conditions D.that fog will soon set in
A.Straight line B.Arc C.Parabola D.Hyperbola