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單項(xiàng)選擇題Large crosshead type engine generally has two lubrication systems, a function performed only by crankcase oil system is（）

A.lubricating
B.cooling
C.cleaning
D.neutralizing

1.單項(xiàng)選擇題Large crosshead type engine generally has two lubrication systems, a function performed only by cylinder oil system is（）

A.lubricating
B.cooling
C.sealing
D.cleaning

2.單項(xiàng)選擇題In some diesel engine designs,（）the injection of cylinder oil is timed to impinge when the piston and only impinge on（）

A.is coming upward；cylinder ring belt
B.is going downward；piston ring belt
C.is coming upward；piston ring belt
D.is going downward；cylinder ring belt