单项选择题
The main purpose of the piston oil scraper rings is to （）.
A.seal the space between the piston and the liner B.reduce the amount of lube oil burned in the combustion chamber C.transmit heat from the piston to the cylinder liner D.damp out fluctuations of the piston side thrust
单项选择题 Maximum horsepower of a diesel engine is attained （）.
单项选择题 Engine protection by means of an alarm or shutdown control can be obtained with devices that are sensitive to （）.
单项选择题 In diesel engines, the four basic events (intake, compression, power and exhaust) are performed once in （）.
