单项选择题
The over-speed trip device installed in some diesel engines is automatically actuated by（）
A.spring force B.hydraulic pressure C.centrifugal force D.mechanical linkage
单项选择题 The flywheel reduces speed fluctuations by （）
单项选择题 How often should the lubricating oil of a diesel engine be changed?（）
单项选择题 The main function of piston compression rings is to （）
