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（）.

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

单项选择题A fixed carbon dioxide extinguishing system for a machinery space，designed WITHOUT a stop valve in the line leading to the protected space，is actuated by（）.

A.one control
B.two controls
C.three controls
D.none of the above

单项选择题A fishing vessel displaying the lights shown is（）.

A.anchored
B.underway but not fishing
C.tending a small fishing boat
D.fishing by trawling

单项选择题A fishing vessel casualty must be reported to the Coast Guard if it involves（）.

A.loss of life
B.an injury requiring only first aid
C.$(SA)10，000 in property damage
D.loss of equipment which doesn't reduce the vessel's maneuverability

单项选择题A fire pump may be used for other purposes if（）.

A.the other services are run off a reducing station with a pressure gage
B.one of the required pumps is kept available for use on the fire main system at all times
C.no relief valves are installed
D.all of the above conditions are met