单项选择题
Excessive lube oil consumption can result from worn or broken（）
A.piston rings B.valve guides C.valve seals D.all of the above
单项选择题 In an operating diesel engine, pre-ignition can be caused by （）
单项选择题 One cause of diesel engine surging can be a result of （）
单项选择题 Cooling water pumps driven by direct reversing diesel engines are usually of the straight impeller vane type pump with a concentric housing to（）
