Gas exchange, which is a basic part of the cycle of an internal combustion engine, is（）

单项选择题“The use of a poor quality oil can lead to rapid deterioration of its properties with the resultant formation of deposits in the piston crown which in turn results in a considerable reduction in heat transfer with subsequent overheating and thermal cracking” According to this sentence, we can know that the principle reason of the overheating and thermal cracking is（）

A.the use of a poor quality oil
B.the deterioration of its properties
C.the formation of deposits
D.the reduction in heat transfer ability

单项选择题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

单项选择题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

单项选择题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

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