A safe water daymark has what shape? （）

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.area of a channel where passing another vessel is permitted

A.two towing lights in a vertical line
B.a towing light in a vertical line above the sternlight
C.two towing lights in addition to the sternlight
D.a small white light in lieu of the sternlight

A.a vessel restricted in her ability to maneuver
B.a vessel under command
C.a passenger ship
D.a seaplane on the water