What is it called when it is possible to ignite the vapour above the oil?（）

Your vessel is docking, but not yet alongside. Which line will be the most useful when maneuvering the vessel alongside the pier?（）.

Full details of all lights and fog signals are shown on（）.

Despite the rising importance and great convenience of the gyrocompass,the magnetic compass still retain its importance because of its（）.

（）is halfway between the forward and after perpendiculars and is reference point for vessel construction.