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

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

单项选择题A frame with two，or sometimes four，arms through which are threaded the guidelines and which is used to keep the drill stem and bit in line with the center opening in the temporary guide base is the（）.

A.drill stem guide
B.guide frame
C.drill string frame
D.casing guide

单项选择题A flooded leg on a liftboat would adversely affect the vessel’s stability underway by（）.

A.increasing the righting moment
B.decreasing the vessel's displacement
C.increasing the reserve buoyancy
D.shifting the CG (center of gravity) off center