單項選擇題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


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1.單項選擇題（）diesel engines generally have two systems of lubrication:（）a total loss system feeding and a circulating system lubricating the running gear and cooling the pistons.

A.Large crosshead type；crossheads
B.High speed；the cylinders
C.Large crosshead type；the cylinders
D.Four-stroke；pistons and cylinders

2.單項選擇題The following options are all the functions of lubricating oil except（）

A.removing heat and deposits
B.neutralizing acidic products
C.lubricating
D.improving combustion efficiency

3.單項選擇題The air distributor is conventionally driven by（） and distributes into each cylinder by（） certain sequence.

A.camshaft；fresh air
B.camshaft；starting air
C.electronic motor which is controlled by a computer；fresh air
D.electronic motor which is controlled by a computer；starting air

4.單項選擇題When an engine is starting and has got a sufficiently high speed, say about 20 rpm,（）

A.the starting air supply is cut off and fuel is injected into the cylinders
B.the fuel feeding is cut off and the turning gear is put in
C.the starting air supply is cut off and turning gear is taken out
D.the electric blower is shut down and fuel is injected into the cylinders

5.單項選擇題When starting an engine, the compressed air enters the cylinder when the corresponding piston is in position of its（）

A.suction stroke
B.compression stroke
C.power stroke
D.exhaust stroke