A.is coming upward；cylinder ring beltB.is going downwar……

单项选择题（）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

单项选择题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

单项选择题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

单项选择题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

单项选择题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