When liquid is free to move transversely in a tank，the effect is called（）.

A.Land first sighted when vessel approaching from seaward
B.Land last sighted when vessel leaving from a port
C.In sight of one another when vessel underway
D.In sight of an island during a ship on her voyage

A.black and green bands
B.red and green bands
C.red and yellow bands
D.yellow and green bands

A.channel junctions
B.bifurcations
C.fishing traps
D.wrecks or obstructions