【单选】In some cases, when _____ exceeds a pre-set value ,the filter is automatically back flushed with air ,the displaced oil going to auxiliary drain tank where it is subsequently filtered and pumped back into the system A.the differential temperatureB.the differential pressureC.the temperature and pressureD.the pressure【单选】'Insufficiency of manning or insufficiency of certification of seafarers' is an identification of a/an ______.A.substandard shipB.standard shipC.over-standard shipD.reference ship【单选】'Loop,' 'uniflow,' 'crossflow,' and 'return-flow' are terms used to describe various types of ______.A.control air circuitsB.superchargingC.turbochargersD.scavenging【单选】 A DC generator is used to supply direct current in order to maintain an AC generator field and is known as a/an ______.A.rotorB.statorC.exciterD.armature【单选】 A centrifuge arranged to separate two liquids is known as _____.A.an oily water separatorB.a purifierC.a centrifugal compressorD.a clarifier【单选】 A circuit breaker and a fuse have a basic similarity in that they both ______.A.can be reset to energize the circuitB.should open the circuit when overloadedC.will burn out when an over current flow developsD.should short the circuit when overloaded【单选】 A circuit breaker differs from a fuse in that a circuit breaker ______.A.melts and must be replacedB.is enclosed in a tube of insulating material with metal ferrules at each endC.gives no visual indication of having opened the circuitD.trips to break the circuit and may be reset【单选】 A circuit breaker is ______.A.a distribution device B.a lighting equipmentC.the indicating instrumentD.an isolating switch【单选】 A combination combustible gas and oxygen indicator is an instrument that measures the _____ of both combustible gas and oxygen; each is indicated on a separate binationsC.concentrationD.filters【单选】 A diesel engine with a combustion chamber located between the crowns of two pistons is known as a/an ______.A.double-acting engineB.opposed pistons engineC.single-acting engineD.horizontal acting engine【单选】 A fire involving aluminum powder would be a class _________. A.'A' fireB.'B' fireC.'C' fireD.'D' fire【单选】 A hydraulic motor may be driven by ______.A.an electric motorB.a diesel engineC.a compressorD.oil【单选】 A marine diesel engine is started by______.A.supplying high pressure oil into a hydraulic motorB.supplying high temperature air into the cylinderC.supplying high pressure air into the cylinderD.electrical igniting【单选】 A positive displacement pump is that where the volume of the pump chamber is alternately increased to ___ and then decreased to ___. A.draw the liquid in / force the liquid outB.force the liquid out / draw the liquid inC.suction/drawD.deliver/outlet【单选】 A practical way of checking for excessive fuel injection in one cylinder of an operating diesel engine is to ______.A.feel the high pressure fuel lineB.check the cylinder exhausts for white smoke frequentlyC.check the cylinder exhaust temperatureD.isolate each cylinder and inspect the injector【单选】 A segregated ballast system is a system where ______.A.all ballast is processed through the oily water separatorB.ballast is taken on and discharged through a separate main deck riserC.ballast and cargo tanks are separated by cofferdamsD.all ballast lines, tanks, and pumps are independent of those used for oil【单选】 A supercharged diesel engine, when compared to a similar naturally aspirated diesel engine, will develop an increase in ______.A.ignition lagB.engine horsepowerC.lube oil system pressureD.specific fuel consumption【单选】 A viscosity regulator used for an engine is usually provided in order to _____ for an engine burning heavy fuel oil.A.regulate the fuel supplyB.maintain a constant fuel viscosity at the fuel valvesC.maintain efficient coolingD.alter the fuel density【单选】According to STCW, the abilities specified in the standards of competence are grouped as seven functions at three levels of responsibility, which of the following is not one of the three levels?A.Navigational levelB.Management levelC.Operational levelD.Support level【单选】According to the MARPOL CODE, glass, metal and paper materials should ______.A.never be discharged into seaB.be discharged beyond 12 nm from nearest landC.be discharged limited in 12 nm from nearest landD.be discharged to sea【单选】According to the SOLAS convention, the bilge water system ______A.The bilge pump must connect the bilge well suction directlyB.should not pump out the water accumulated in the cargosC.should not be used for emergency drainage in case of ship collisionD.should be connected to the fire fighting system directly【单选】After 'F.W.E.' is given, the air system is shut down, the _____ gear put in, all drains and indicator cocks opened, and the cooling water kept running.A.steeringB.timingC.turningD.running【单选】After 'finished with engine', which of the following cannot be shut off by the duty engineer ?A.fuel oil booster pumpB.the main starting valveC.the sea chestD.the main cooling sea water pump【单选】After taking on fuel oil, the hoses should be disconnected and ______.A.draped over the fantail to dry outB.drained over the side and washed outC.drained into the bilges and washed outD.drained into buckets【单选】Air chambers are usually fitted to reciprocating pumps in order to ___.A.increase discharge pressureB.increase suction vacuumC.develop pulsation flowD.keep a steady rate of flow【单选】All crew's assigned emergency stations can be found on the ship's ______.A.muster listB.certificate of inspectionC.clearance papersD.permit to proceed【单选】All details of fuel bunkering or slop disposal must be entered in the _____.A.rough logB.engine room log bookC.oil record bookD.smooth log【单选】An emergency generator, driven by an internal combustion engine, shall be tested under load for a minimum of 2 hours at least once every ______.A.weekB.2 weeksC.monthD.3 months【单选】An incinerator auxiliary burner can not be ignited. It is NOT caused by______.A.carbon deposits on the electrodesB.defective atomizerC.low oil pressureD.too much water in the oil sludge【单选】An incinerator auxiliary oil-fired burner is used to ignite ______.A.the solidwaste or the oil sludgeB.the solid waste onlyC.the oil sludge onlyD.neither the solid waste nor the oil sludge【单选】Anchor capstans are used in some installation where the cable lifter rotates about a ______. A.horizontal axisB.crankshaftC.vertical axisD.camshaft【单选】As for oil separator, ______contributes to poor separation efficiency and carries over of water into the clean oil outlet.A.A too big gravity discB.A too small gravity discC.The high oil temperatureD.The high speed motor【单选】As the amount of moisture in the air increases, the difference between the dry bulb and wet bulb temperatures will ______.A.increaseB.decreaseC.remain unchangedD.be greatest at dew point【单选】Before doing any work on a hydraulic system equipped with accumulators, you should ______.A.drain the accumulators and purge with oxygenB.bleed off all stored energy from the accumulators completely C.charge the accumulators to prevent system energy lossD.pump the hydraulic fluid into the accumulators to prevent fluid loss【单选】Before starting the engine, the air bottle should be ______.A.pumped up B.loaded C.discharged D.closed【单选】Biological sewage water treatment plant work on the_____.A.heating processB.settling processC.aeration processD.centrifuging process【单选】Cargo handling unit is rated according to the _____ to be lifted.A.cargo craneB.jibC.safe working loadD.oil pressure【单选】Centrifugal pumps, used to handle hot liquids, must have a minimum flow through them under all operating conditions. This flow serves to ______.A.prevent overheating and damage to pump rotating parts due to rubbingB.maintain the net positive suction head of the pumpC.maintain hydraulic differential in the pump impeller passagesD.purge the pump of non-condensable vapors and gases【单选】Coalescence is the breakdown of surface tension between oil droplets in an oil/water mixture, which causes them to join and _____ in size.A.expand B.extract C.increase D.decrease【单选】Combustion gases formed in the cylinder of a diesel engine are prevented from blowing past the piston by ______.A.cylinder pression ringsC.piston skirtsD.oil rings【单选】Cooling of engines is achieved by circulating a cooling liquid around internal ______ within the engine.A.airB.passagesC.pipesD.means【单选】Dual electro-hydraulic steering units usually operate ______.A.with both pumps on line at the same timeB.with one pump on standbyC.with the follow-up gear disconnectedD.only when the rudder is moved amidships【单选】During ______ the gases are driven out of the cylinder by the piston.A.The suction strokeB.The compression strokeC.The expansion strokeD.the exhaust stroke【单选】During purification, if the operating water tank is empty, which of the following malfunctions will appear?A.Some oil will flow from the water outlet of the separator.B.There will be some water in the purified oil.C.Some oil will flow from the sludge outlet of the separator.D.If discharging the sludge, there will be no flushing water.【单选】Each crank is made up of two crank webs joined by a common ______ to which the bottom end bearing is fitted. A.throw B.crankshaft C.crankpin D.crosshead【单选】Each cylinder liner on the marine medium speed engines _____. A.is usually cooled by sea water B.can be replaced when worn out C.is in direct contact with the water in the bore of the cylinder D.can't expand when heated【单选】Electric wires should have each feature of the following except ______.A.flame retardantB.moisture resistantC.oil resistant D.low conductivity【单选】Engine speeds at which resonance can occur are termed ______.A.maximum speedsB.full speedsC.sea speedsD.critical speeds【单选】Equal power factors on paralleled AC generators are maintained by an automatic ________.A.voltage regulatorB.reverse power relayC.reverse current ernor control switch【单选】Failure to open the diesel engine test cocks after a long period of shutdown, prior to starting may result in _______.A.an air bound fuel systemB.damage to cylinder heads and pistonsC.excessive fuel injectionD.excessive air valve lift【单选】Fuel droplets injected into a diesel engine cylinder must have adequate penetration to ______.A.prolong the ignition delay periodB.ensure the beginning of fuel injectionC.thoroughly utilize the air chargeD.allow controlled fuel combustion【单选】Fuel is ignited into a diesel engine cylinder by ______.A.a spark plugB.injectorsC.the heat of compressionD.increasing jacket water temperatures【单选】Full travel of the electronic governor actuator linkage must exceed the ______ travel of the engine fuel control to ensure that the engine fuel control is capable of moving from the 'off' position to 'full fuel'. A.minimumB.averageC.maximumD.half【单选】Heavy residual fuel oils are heated prior to centrifuging to ______.A.reduce fuel weightB.increase specific gravityC.separate fuel from lube oilD.reduce fuel viscosity【单选】How can the chance of contaminating hydraulic fluid be decreased when working on hydraulic systems?A.Clean the fittings before they are disconnected.B.Place drip pans under leaky fittings.C.Seal any cracks in lines with Permatex.D.Coat all threads with graphite oil. 【单选】ISM code has applied to the ships as follows exceptA.Passenger shipsB.Bulk freight vessels of 500 gross tons or moreC.Warship of 500 gross tons or moreD.High-speed craft of 500 gross tons or more【单选】If a cam-controlled engine has a normal injection pressure at rated speed, the injection pressure will be ______ at slow speed.A.a little lower B.a little higherC.too lowD.exactly the same【单选】If a fire ignites in the engine room as a result of a high pressure fuel oil leak, you should FIRST ______.A.secure the ventilationB.find a soda acid extinguisherC.shut off the fuel oil supplyD.secure the generator【单选】If an oil spill occurs on deck, you should ______.A.cover the area with foamB.cover the area with absorbent materialC.wash down immediately with a fire hoseD.wash down immediately with an oil dispersing solvent【单选】If found oil when we open low oil level plug of separator, it indicates _______.A.the separator is overloadedB.the monitor equipment of separator failsC.the discharge pump of separator can not workD.the temperature of oil water is low【单选】If the engine is at rest during maneuver for an extended period the engine should _______, of course, that navigational circumstances permit, before restarting on fuel.A.be turned on airB.be tried on powerC.be turned by the turning gearD.be tested on fuel【单选】If the pump for a hydraulic anchor windlass is overheating, the cause may be ______.A.increased pump speedB.excessive pump discharge pressureC.too low of a tilting box angleD.low pump speed【单选】If the sea water supply pressure for a diesel engine cooling system is below normal, you should check for a ______.A.broken thermostatB.clogged sea water strainerC.blown head gasketD.cracked head【单选】If the speed of a turbocharged diesel engine is maintained constant as the load on the engine is increased, the speed of the turbocharger will ______.A.decrease until the engine speed increasesB.increaseC.decreaseD.remain unchanged【单选】If you heard a 'crackling' noise in a centrifugal pump, the most probable cause of the problem would be ______.A.insufficient speedB.cavitationC.excess discharge pressureD.excessive net positive suction head【单选】Immediately after any diesel engine is started, the engineer should check the ______.A.crankcase pressureB.lube oil pressureC.saltwater pressureD.exhaust temperature【单选】In Maritime Labour Convention, hours of rest may be divided into no more than two periods, one of which shall be at least ___ hour in length, and the interval between consecutive periods of rest shall not exceed 14 hours.A.fourB.fiveC.sixD.seven【单选】In ___ pumps a closed discharge valve will cause bursting discharge pressure.A.centrifugalB.plungerC.injectorD.water【单选】In ______ the control action is independent of the output.A.a closed loop control system B.an open loop control systemC.a boiler control system D.a steering gear control system【单选】In a diesel engine cooling water system, a pH of 6.0 indicates a/an ______.A.slightly acidic conditionB.slightly alkaline conditionC.over-treatment of waterD.neutral condition of water【单选】In a general cargo crane, _____ is fitted to lift the cargo load.A.the slewing motorB.the luffing motorC.the hoisting motorD.the fan motor【单选】In a radial piston pump, reversal and control of fluid flow are accomplished by moving the _______. A.central valveB.radial plungerC.floating ringD.cylinder body【单选】In an air conditioning system, moisture is removed from the air by ______.A.filtersB.separatorsC.ducted trapsD.dehumidifiers【单选】In common rail engines, the fuel is ______ before is injected into the cylinders.A.stored in a common fuel lineB.pumped by the injection pumpC.at low pressureD.already atomized【单选】In some diesel engine designs, the injection of cylinder oil is timed to impinge when the piston is coming upward and only impinge on ______.A.piston skirtB.piston crownC.piston ring belt.D.cylinder ring belt【单选】In the Oil Record Book, a comprehensive list of operational items are grouped into operational sections. Each section is codified by a/an ______.A.numberB.abbreviationC.letterD.number、abbreviation and letter【单选】In the electronic governor actuator, the oil pressure is provided by a ______ pump driven by a shaft connected to the engine camshaft.A.servomotorB.hydraulic motorC.gearD.volute【单选】In the event of a small bunker oil spill on deck occurring while bunkering, youshould ______.A.wash down the area immediately with a fire hoseB.wash down the area with keroseneC.cover the area with absorbent materialD.cover the area with foam【单选】In the event of minor emergencies when the machinery spaces unattended, ______ will be informed of malfunctions in the machinery by his cabin monitor.A.the chief engineerB.the engineer on cabin watchC.the bridge officer on watchD.the master【单选】In the production of freshwater from seawater through a process of heating and cooling, the cooling phase of production is usually called ______.A.evaporationB.distillationC.dehydrationD.condensation【单选】Increasing the temperature of a fuel will _____ its viscosity, and vice-versa.A.increaseB.not changeC.reduceD.add【单选】It ______ for an emergency generator to require paralleling.A.is usual B.is not usualC.is necessaryD.is not impossible【单选】It is important to note that when an excessive amount of water is present in the fuel the temperature for centrifuging must be kept below ______, otherwise forming and agitation of the fuel takes place.A.the condensating point of waterB.the boiling point of waterC.the flash point of the fuelD.the flammable point of the fuel【单选】It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong direction. This would cause the pump ______.A.head capacity to improveB.discharge to be reversedC.efficiency to decreaseD.slippage to decrease【单选】Leakage of hydraulic fluid from around the shaft of a hydraulic motor may be caused by ______.A.permanent loss of pump suctionB.worn shaft sealsC.high level in the oil sumpD.low motor RPM【单选】Loss of lubricating oil pressure to the main propulsion diesel engine will actuate a/an ______.A.over-speed tripB.audible/visual alarmC.the ships/boats general alarmD.reserve oil storage tank【单选】Maintaining the lowest possible scavenging air temperature at all times is not recommended due to the possibility of the ______.A.air charge density becoming too highB.piston crown surfaces becoming too coldC.formation of excessive quantities of pression pressure being greatly reduced【单选】Maximum pressure readings should be taken when the engine is running on ______ as steadily as possible.A.half loadB.full loadC.average loadD.minimum load【单选】Motor controllers are seldom troubled with grounds because ______.A.the auxiliary contacts have a high resistance connectionB.the contactors and relays are mounted on a non-conducting panelC.the resistor banks are composed of individual series-connected unitsD.there are separate switches for the motor and the control【单选】Noxious emissions amount to 0.25～0.4 percent by volume of the exhaust gas, depending on the amount of ______ in the fuel and its lower heat value, and the engine type, speed and efficiency.A.carbonB.sulphurC.oxidD.water【单选】Over-greasing of ball bearings installed on pumps will result in ______.A.smoother pump operationB.overheating of the bearingC.reduced corrosion in the bearingD.increased pump capacity【单选】Owing to its __________, the low speed cross-head diesel engine is widely used on board ship as a main engine.A.smaller size and simple constructionB.long life, lower cost and reliabilityC.easier operation and managementD.simple construction and easier management【单选】Prior to closing the breaker when paralleling two AC generators, the recommended practice is to have the frequency of the incoming machine ______.A.slightly less than the line frequencyB.the same as the line frequencyC.slightly greater than the line frequencyD.have nothing to do with the line frequency【单选】Prior to starting, the purpose of turning over a main propulsion diesel engine with the cylinder test cocks open, is to ______.A.test the starting systemB.remove condensation from the cylindersC.check the compressionD.check for proper lube oil pressure【单选】Reheating a hardened component to a temperature lower than the hardening temperature and then cooling it is known as ______.A.low temperature hardeningB.case hardeningC.annealingD.tempering【单选】Remote control means that _____ .A.the system is manned manuallyB.the system is situated remotely from the operatorC.the system is controlled automaticallyD.the system is controlled from the bridge【单选】Restrictions occurring in the small orifices of pneumatic control system components can be caused by ______.A.moisture in the compressed air supplyB.excessive dryness in the compressed air supplyC.pressure surging in the compressed air receiverD.insufficient lubrication of the system components【单选】STCW Convention describes that _____ are laid down for the certification of engineer officers in charge of a watch in a traditionally manned engine room, or the designated engineer in a periodically unmanned engine room. A.available minimum requirementsB.available maximum requirementsC.mandatory minimum requirementsD.mandatory maximum requirements【单选】STCW Convention states that the officer in charge of the engineering watch is the _____ representative.A.ship-owner'sB.master'sC.chief engineer'sD.manager's【单选】Safe working conditions inside the crankcase are ______, especially for large bore engines where the components are quite heavy.A.reliableB.safetyC.easyD.important【单选】Seawater can be used for drinking ______. A.at a maximum rate of two ounces per dayB.after mixing with an equal quantity of fresh waterC.if gather during or immediately after a hard rainD.under no circumstance【单选】Smaller equipment may be supplied via ______ or miniature circuit breakers.A.exciters mutatorsC.fusesD.wattmeter【单选】The Abbreviation "ERM" in the Manila Amendments to the STCW Convention stands for ______.A.Engine Room ManagementB.Engine Resources ManagementC.Engineer Resources ManagementD.Engine-room Resources Management【单选】The ISM Code is a part of ____.A.SOLASB.MARPOLC.STCWD.Ballast Water convention【单选】The International Management Code for the Safe operation of ships and for Pollution Prevention is referred to as _______.A.ISM CodeB.IOPP CodeC.IMS CodeD.ISPS Code 【单选】The Port Authorities, in accordance with the IMO resolutions have been carrying out _____ to enhance safety of foreign ships.A.CPP B.FPP C.PSC D.FSC【单选】The SMS should provide for specific measures aimed at promoting the_____ of equipment or systems, the sudden operational failure of which may result in hazardous situations.A.visibilityB.abilityC.reliabilityD.capability【单选】The ______of the telemotor is mounted on the steeringgear.A.transmitterB.receiverC.pipesD.charging unit【单选】The ability of lubricating oils to resist viscosity changes during temperature changes is indicated by the ______.A.American Petroleum B.Institute number viscosity index numberC.Seconds Saybolt Furol numberD.Seconds Saybolt Universal number【单选】The activated sludge strength should be checked at regular intervals, and it is good that the color of the aeration compartment water is ______.A.chocolateB.yellowC.blackishD.ivory-white【单选】The air distributor is conventionally driven by ______ and distributes ______ into each cylinder by certain sequence.A.camshaft / fresh airB.camshaft / starting airC.electronic motor which is controlled by a computer / fresh airD.electronic motor which is controlled by a computer / starting air【单选】The burning of ______ is a class‘C’fire.A.diesel oilB.magnesiumC.dunnageD.electrical insulation【单选】The capacity of the supply pump to the separator should correspond with the recommended throughput, or it must be adjusted without the risk of ______ formation.A.sludgeB.emulsionC.oil runoutD.deposit【单选】The clutch band of a constant tensioning mooring winch must be set up tight enough to drive the winch drum and should slip only when ______. A.excessive loads are placed on the winch B.minimum pull is being exerted by the winch C.automatic operation of the winch is desired D.wire is being retrieved at the maximum rate【单选】The cooling water jacket is common to all the cylinders but there are often ______ to ensure that each cylinder receives the right amount and flow of water. A.dividing walls B.divided walls C.dividing liners D.divided jackets【单选】The descriptions about cetane number are TRUE except ______.A.Cetane number indicates ignition qualityB.The lower value the cetane number is of, the poorer the ignition quality will beC.Cetane number isn't the only measurement of ignition quality.D.Cetane number is measured by Redwood instrument【单选】The device that most commonly utilizes the principle of electromagnetic induction is the ______.A.diodeB.transformerC.transistorD.rheostat【单选】The engineer officer in charge of the watch shall ensure that ______are kept under constant surveillance.A.the devices and systems in chargeB.the communication devicesC.the main propulsion plant and auxiliary systemsD.the steering gear【单选】The expansion tank for a diesel engine closed cooling system is designed to maintain a constant head on the system and ______.A.reduce water temperatureB.reduce water turbulenceC.provide an air cushionD.allow for an increase in water volume as the engine warms up【单选】The extended aeration process consists of _____ the liquor either by bubbling air through it or by agitating the surface.A.deoxygenating B.oxygenatingC.chemicalizingD.disinfecting【单选】The frequency output of an operating alternator is controlled by the ______.A.relative speed of the rotor polesB.number of turns of wire in the armature coilC.strength of the magnets usedD.output voltage【单选】The instrument which the emergency switchboard doesn't need is ______.A.ammeter B.voltageC.wattmeterD.synchronous meter【单选】The load sharing characteristics of two diesel generators operating in parallel are mostly dependent on their governor ______.A.load limit settingsB.idle speed settingsC.speed limit settingsD.speed droop settings【单选】The lubricating oil purifier may ______ oil from the drain tank and ______ the clean oil into the supply line.A.take; takeB.discharge; takeC.discharge; dischargeD.take; discharge 【单选】The magnetic field is provided by electromagnets so arranged that adjacent poles have ______.A.opposite polarityB.the same polarityC.negative polarityD.positive polarity 【单选】The main objective of ISPS Code is ______.A.to prevent the human injury and the loss of lifeB.to specify the measures to enhance maritime securityC.to avoid the damage to the environment, particularly to the marine environmentD.to ensure the compliance with conventions【单选】The main objective of the SOLAS Convention is ______.A.to specify minimum standards for the construction, equipment and operation of ships.B.to specify minimum standards for the training, certification and watch keeping for seafarers.C.to provide minimum standards for the operation of vessels.D.to tell the company how to run the business.【单选】The majority of automatic mooring winches are _____ to improve the backward efficiency of the gear train for rendering.A.spur gearedB.screw gearedC.worm gearedD.belt driven【单选】The most critical part of the bunkering operations, which can result in an oil spill, is when the ______.A.hose joints are made upB.tanks are being topped offC.system is being lined upD.pumping operation is first started【单选】The officer in charge of an engineering watch shall have the knowledge of ERM principles, including obtaining and maintaining ______.A.situational awarenessB.safety awarenessC.environmental awarenessD.anti-pollution awareness【单选】The officer in charge of the engineering watch shall ensure that at all times bridge orders relating to changes in _____ of operation are immediately implemented. A.ahead or astern B.fore or aft C.up or down D.speed or direction【单选】The only means of removing the latent heat of condensation from a refrigerant in the normal refrigeration cycle is by ______.A.passing it through the expansion valveB.condensing refrigerant in the system condenserC.passing the gaseous refrigerant through the heat interchanger on the suction side of the compressorD.maintaining a high pressure on the system's receiver【单选】The operator of electrical motors should keep a constant check on the loads they carry because ______.A.low loads necessitate frequent insulation cleaningB.exceeding nameplate values shortens useful lifeC.energy is wasted if full loading is not utilizedD.power factor correction methods are load dependent【单选】The overcurrent relay _____ the motor contactor when the motor exceeds its rated current.A.connectsB.tripsC.foulsD.destructs【单选】The part of a fuse that melts and opens the circuit is made of ______.A.copper and antimonyB.steel and babbittC.aluminum or beryllium alloyD.zinc or an alloy of tin and lead【单选】The piston rod scraper box incorporated in a two-stroke/cycle, crosshead diesel engine serves to ______.A.eliminate the necessity for an oil scraper ringB.prevent side thrust and cylinder scoringC.prevent sludge and dirty oil from entering the crankcaseD.scrape oil。
