單項選擇題Ammonia when used as a refrigerant is valuable because of its high efficiency, it is however （）.

A.toxic
B.flammable
C.explosive
D.all of the above


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1.單項選擇題Which of the following is operated from the main engine room console on an automated vessel?（）

A.Fire pump and lube oil pump
B.Lube oil pump and distilling plant
C.Distilling plant and shaft alley door
D.Shaft alley door and fixed CO2 release

2.單項選擇題An un-loader is installed on an air compressor to （）.

A.bypass the high pressure stage to the low pressure stage on 100% of the air compressors in service
B.prevent excessive inter-stage pressure buildup
C.control compressor discharge pressure
D.remove all but the frictional load during starting

3.單項選擇題After installing a new hydraulic pump in a system, what special attention should be given to the hydraulic system?（）

A.The relief valves in the system should be readjusted
B.The filters and strainers should be checked frequently
C.All system pressure should be readjusted
D.The system should be drained and renewed with a fluid of different operating characteristics

5.單項選擇題One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.

A.maintain radial alignment between the pump impeller and casing
B.absorb all impeller shaft end thrust
C.prevent water leakage to the atmosphere
D.prevent wear of the pump casing and/or impeller