單項(xiàng)選擇題The efficiency and output capacity of a low pressure distilling plant will be reduced if the last effect shell （）

A.pressure does not fluctuate rapidly
B.pressure remains steady and unchanged
C.brine density does not exceed 1~5
D.brine density is too low


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1.單項(xiàng)選擇題In most pumps and pump motors overpacking the ball bearings full of grease will result in （）

A.moisture emulsification of the bearing grease
B.insufficient circulation and overheating of the bearing
C.proper grease circulation to cool the bearing
D.sliding friction between balls and races

2.單項(xiàng)選擇題Aqueous Film Forming Foam (AFFF), commonly known as ‘light water’, is especially suitable for fighting （）

A.oil fires in the engine room bilges
B.class B fires in paint lockers
C.any class D fire
D.all of the above

3.單項(xiàng)選擇題Which of the following statements concerning the water tube and fire tube boilers is not true?（）

A.natural circulation of the water in the water tube boiler is better than that in the fire tube boiler
B.for the same output the water tube boiler will carry less mass of water compared with the fire tube boiler
C.the water tube boiler will cost shorter time for steam raising
D.the water tube boiler require lower skill in operating and maintaining

4.單項(xiàng)選擇題Which one of following statement is not true concerning the suitable sites of the direct acting relief valve and the pilot operated relieve valve?（）

A.the direct acting relief valve is used for controlling lower flows and pressure
B.the pilot operated relief valve is used for controlling higher flows and pressure
C.the pilot operated relief valve is used for controlling lower flows and pressure
D.the controlling accuracy of direct acting relief valve is worse than that of the pilot operated relief valve

5.單項(xiàng)選擇題In heavy marine engine the practice is to drive the engine on（）which has previously been stored in starting air reservoirs.

A.electric motor
B.hydraulic motor
C.compressed air
D.turning gear