Which of the substances listed is satisfactorily removed from the fuel by a centrifugal oil purifier?（）

The most common contaminate of governor hydraulic fluid is （）.

A.moisture
B.dirt
C.acid
D.air

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The purpose of the safety relief valves installed on an auxiliary boiler is to （）.

A.relieve excess fuel oil pressure during the “off” fire cycle
B.admit water to the dry pipe
C.throttle the forced draft fan output for proper combustion
D.reduce excess steam pressure in the boiler

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