單項選擇題A substance found in residual fuels which tends to cause exhaust valve corrosion and grooving, is（）

A.carbon
B.vanadium
C.calcium
D.hydrogen


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1.單項選擇題If the turbocharger of a four-stroke/cycle diesel engine fails to operate, which of the following statements best describes the probable effect?（）

A.Intake manifold pressure will be high
B.Intake manifold pressure will be unaffected
C.Exhaust temperatures will be high
D.Exhaust temperatures will be low

2.單項選擇題The best tool to use for removing the carbon ridge at the top of an enginecylinder, prior to removing the piston, is to use（）

A.an electric grinder
B.a metal scraper
C.a reamer
D.a three-wing hone

3.單項選擇題Which of the following problems can cause an above normal air temperature to develop in the intake manifold of a turbocharged and after-cooled diesel engine?（）

A.Faulty turbocharger turbine diffuser ring
B.Faulty turbocharger compressor ring
C.Insufficient cooling water flow
D.Clogged air intake filters

4.單項選擇題Which of the following conditions can cause below normal air pressure in the intake manifold of a turbocharged diesel engine?（）

A.Excessive piston blow-by to the manifold
B.Insufficient cooling water flow
C.Accumulated water in the air boxes
D.Clogged air intake filters

5.單項選擇題If sludge accumulates on the underside of a diesel engine piston, it will（）

A.cause blow-by
B.chemically attack the piston skirt
C.form an emulsion of lube oil and water
D.raise the piston temperature