A helmsman receives the command “Right 15 degrees rudder.”The helmsman’s IMMEDIATE reply should be（）.

单项选择题A heavy，thick-walled tube，usually steel，used between the drill pipe and the bit in the drill stem to weight the bit in order to improve its performance is called a（）.

A.heavy-walled drill pipe
B.tool joint
C.down hole tool
D.drill collar

单项选择题A heavy steel curved arch constructed athwartships and above the after deck on a towing vessel is sometimes called a（）.

A.main brace
B.tow span
C.jockey bar
D.None of the above

单项选择题A head-on situation at night is one in which you see dead ahead a vessel showing（）.

A.one sidelight
B.one sidelight and a masthead light
C.one sidelight and two masthead lights
D.both sidelights of a vessel and her masthead light(s)

单项选择题A hand held instrument used to measure distances between objects and the ship is a（）.

A.vernier
B.psychrometer
C.hygrometer
D.stadimeter

单项选择题A green buoy has a yellow triangle on it. This is a(n)（）.

A.information or regulatory buoy that has lateral significance
B.buoy that is off-station and is marked to warn mariners of its wrong position
C.dual purpose marking used where the ICW and other waterways coincide
D.buoy that was set in error and will be replaced with a red nun buoy