单项选择题
Valves in the cylinder head of a diesel engine are opened by the direct action of the（）
A.exhaust pressure B.valve spring pressure C.rocker arm movement D.wrist pin movement
单项选择题 On a large diesel engine installation, crankshaft axial alignment is maintained by the （）
单项选择题 A piston is said to be at top dead center when it is （）
单项选择题 During which of the listed piston stroke of a four-stroke/cycle diesel engine, is the piston moving downward?（）
