单项选择题
In order to ensure perfect atomization, the fuel oil () before injection.
	A.has to be cooled
	B.has heated
	C.has preheated
	D.has to be preheated
                    
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 In large marine diesel engines cylinder oils usually contain additives formulated to impart the () to clean the rings and grooves.
 A.inefficiency 
 B.oiliness
 C.detergency
 D.purity
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 In general, () is suitable for delivering small quantities at high pressure.
 A.reciprocating pump 
 B.gear pump
 C.centrifugal pump
 D.vane pump
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                                    单项选择题
                                    
 In four strokes engine, the cycle of events is completed in four strokes of ().
 A.the cylinder 
 B.the crankshaft
 C.the piston
 D.the cross-head
 
             
             
                
            